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author | peter <peter@FreeBSD.org> | 1995-12-30 19:02:48 +0000 |
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committer | peter <peter@FreeBSD.org> | 1995-12-30 19:02:48 +0000 |
commit | 3c2e7478e1136c470620ae4525a8aceaf8db8b8c (patch) | |
tree | f639bcf9350fe5685370933c19a11ce590271dd2 /gnu/usr.bin | |
parent | c21193cc8a2bb711bec796d1f309d49f4a8ca8cb (diff) | |
download | FreeBSD-src-3c2e7478e1136c470620ae4525a8aceaf8db8b8c.zip FreeBSD-src-3c2e7478e1136c470620ae4525a8aceaf8db8b8c.tar.gz |
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diff --git a/gnu/usr.bin/awk/gawk.texi b/gnu/usr.bin/awk/gawk.texi deleted file mode 100644 index b280262..0000000 --- a/gnu/usr.bin/awk/gawk.texi +++ /dev/null @@ -1,11270 +0,0 @@ -\input texinfo @c -*-texinfo-*- -@c %**start of header (This is for running Texinfo on a region.) -@setfilename gawk.info -@settitle The GAWK Manual -@c @smallbook -@c %**end of header (This is for running Texinfo on a region.) - -@ifinfo -@synindex fn cp -@synindex vr cp -@end ifinfo -@iftex -@syncodeindex fn cp -@syncodeindex vr cp -@end iftex - -@c If "finalout" is commented out, the printed output will show -@c black boxes that mark lines that are too long. Thus, it is -@c unwise to comment it out when running a master in case there are -@c overfulls which are deemed okay. - -@iftex -@finalout -@end iftex - -@c ===> NOTE! <== -@c Determine the edition number in *four* places by hand: -@c 1. First ifinfo section 2. title page 3. copyright page 4. top node -@c To find the locations, search for !!set - -@ifinfo -This file documents @code{awk}, a program that you can use to select -particular records in a file and perform operations upon them. - -This is Edition 0.15 of @cite{The GAWK Manual}, @* -for the 2.15 version of the GNU implementation @* -of AWK. - -Copyright (C) 1989, 1991, 1992, 1993 Free Software Foundation, Inc. - -Permission is granted to make and distribute verbatim copies of -this manual provided the copyright notice and this permission notice -are preserved on all copies. - -@ignore -Permission is granted to process this file through TeX and print the -results, provided the printed document carries copying permission -notice identical to this one except for the removal of this paragraph -(this paragraph not being relevant to the printed manual). - -@end ignore -Permission is granted to copy and distribute modified versions of this -manual under the conditions for verbatim copying, provided that the entire -resulting derived work is distributed under the terms of a permission -notice identical to this one. - -Permission is granted to copy and distribute translations of this manual -into another language, under the above conditions for modified versions, -except that this permission notice may be stated in a translation approved -by the Foundation. -@end ifinfo - -@setchapternewpage odd - -@c !!set edition, date, version -@titlepage -@title The GAWK Manual -@subtitle Edition 0.15 -@subtitle April 1993 -@author Diane Barlow Close -@author Arnold D. Robbins -@author Paul H. Rubin -@author Richard Stallman - -@c Include the Distribution inside the titlepage environment so -@c that headings are turned off. Headings on and off do not work. - -@page -@vskip 0pt plus 1filll -Copyright @copyright{} 1989, 1991, 1992, 1993 Free Software Foundation, Inc. -@sp 2 - -@c !!set edition, date, version -This is Edition 0.15 of @cite{The GAWK Manual}, @* -for the 2.15 version of the GNU implementation @* -of AWK. - -@sp 2 -Published by the Free Software Foundation @* -675 Massachusetts Avenue @* -Cambridge, MA 02139 USA @* -Printed copies are available for $20 each. - -Permission is granted to make and distribute verbatim copies of -this manual provided the copyright notice and this permission notice -are preserved on all copies. - -Permission is granted to copy and distribute modified versions of this -manual under the conditions for verbatim copying, provided that the entire -resulting derived work is distributed under the terms of a permission -notice identical to this one. - -Permission is granted to copy and distribute translations of this manual -into another language, under the above conditions for modified versions, -except that this permission notice may be stated in a translation approved -by the Foundation. -@end titlepage - -@ifinfo -@node Top, Preface, (dir), (dir) -@comment node-name, next, previous, up -@top General Introduction -@c Preface or Licensing nodes should come right after the Top -@c node, in `unnumbered' sections, then the chapter, `What is gawk'. - -This file documents @code{awk}, a program that you can use to select -particular records in a file and perform operations upon them. - -@c !!set edition, date, version -This is Edition 0.15 of @cite{The GAWK Manual}, @* -for the 2.15 version of the GNU implementation @* -of AWK. - -@end ifinfo - -@menu -* Preface:: What you can do with @code{awk}; brief history - and acknowledgements. -* Copying:: Your right to copy and distribute @code{gawk}. -* This Manual:: Using this manual. - Includes sample input files that you can use. -* Getting Started:: A basic introduction to using @code{awk}. - How to run an @code{awk} program. - Command line syntax. -* Reading Files:: How to read files and manipulate fields. -* Printing:: How to print using @code{awk}. Describes the - @code{print} and @code{printf} statements. - Also describes redirection of output. -* One-liners:: Short, sample @code{awk} programs. -* Patterns:: The various types of patterns - explained in detail. -* Actions:: The various types of actions are - introduced here. Describes - expressions and the various operators in - detail. Also describes comparison expressions. -* Expressions:: Expressions are the basic building - blocks of statements. -* Statements:: The various control statements are - described in detail. -* Arrays:: The description and use of arrays. - Also includes array-oriented control - statements. -* Built-in:: The built-in functions are summarized here. -* User-defined:: User-defined functions are described in detail. -* Built-in Variables:: Built-in Variables -* Command Line:: How to run @code{gawk}. -* Language History:: The evolution of the @code{awk} language. -* Installation:: Installing @code{gawk} under - various operating systems. -* Gawk Summary:: @code{gawk} Options and Language Summary. -* Sample Program:: A sample @code{awk} program with a - complete explanation. -* Bugs:: Reporting Problems and Bugs. -* Notes:: Something about the - implementation of @code{gawk}. -* Glossary:: An explanation of some unfamiliar terms. -* Index:: -@end menu - -@node Preface, Copying, Top, Top -@comment node-name, next, previous, up -@unnumbered Preface - -@iftex -@cindex what is @code{awk} -@end iftex -If you are like many computer users, you would frequently like to make -changes in various text files wherever certain patterns appear, or -extract data from parts of certain lines while discarding the rest. To -write a program to do this in a language such as C or Pascal is a -time-consuming inconvenience that may take many lines of code. The job -may be easier with @code{awk}. - -The @code{awk} utility interprets a special-purpose programming language -that makes it possible to handle simple data-reformatting jobs easily -with just a few lines of code. - -The GNU implementation of @code{awk} is called @code{gawk}; it is fully -upward compatible with the System V Release 4 version of -@code{awk}. @code{gawk} is also upward compatible with the @sc{posix} -(draft) specification of the @code{awk} language. This means that all -properly written @code{awk} programs should work with @code{gawk}. -Thus, we usually don't distinguish between @code{gawk} and other @code{awk} -implementations in this manual.@refill - -@cindex uses of @code{awk} -This manual teaches you what @code{awk} does and how you can use -@code{awk} effectively. You should already be familiar with basic -system commands such as @code{ls}. Using @code{awk} you can: @refill - -@itemize @bullet -@item -manage small, personal databases - -@item -generate reports - -@item -validate data -@item -produce indexes, and perform other document preparation tasks - -@item -even experiment with algorithms that can be adapted later to other computer -languages -@end itemize - -@iftex -This manual has the difficult task of being both tutorial and reference. -If you are a novice, feel free to skip over details that seem too complex. -You should also ignore the many cross references; they are for the -expert user, and for the on-line Info version of the manual. -@end iftex - -@menu -* History:: The history of @code{gawk} and - @code{awk}. Acknowledgements. -@end menu - -@node History, , Preface, Preface -@comment node-name, next, previous, up -@unnumberedsec History of @code{awk} and @code{gawk} - -@cindex acronym -@cindex history of @code{awk} -The name @code{awk} comes from the initials of its designers: Alfred V. -Aho, Peter J. Weinberger, and Brian W. Kernighan. The original version of -@code{awk} was written in 1977. In 1985 a new version made the programming -language more powerful, introducing user-defined functions, multiple input -streams, and computed regular expressions. -This new version became generally available with System V Release 3.1. -The version in System V Release 4 added some new features and also cleaned -up the behavior in some of the ``dark corners'' of the language. -The specification for @code{awk} in the @sc{posix} Command Language -and Utilities standard further clarified the language based on feedback -from both the @code{gawk} designers, and the original @code{awk} -designers.@refill - -The GNU implementation, @code{gawk}, was written in 1986 by Paul Rubin -and Jay Fenlason, with advice from Richard Stallman. John Woods -contributed parts of the code as well. In 1988 and 1989, David Trueman, with -help from Arnold Robbins, thoroughly reworked @code{gawk} for compatibility -with the newer @code{awk}. Current development (1992) focuses on bug fixes, -performance improvements, and standards compliance. - -We need to thank many people for their assistance in producing this -manual. Jay Fenlason contributed many ideas and sample programs. Richard -Mlynarik and Robert J. Chassell gave helpful comments on early drafts of this -manual. The paper @cite{A Supplemental Document for @code{awk}} by John W. -Pierce of the Chemistry Department at UC San Diego, pinpointed several -issues relevant both to @code{awk} implementation and to this manual, that -would otherwise have escaped us. David Trueman, Pat Rankin, and Michal -Jaegermann also contributed sections of the manual.@refill - -The following people provided many helpful comments on this edition of -the manual: Rick Adams, Michael Brennan, Rich Burridge, Diane Close, -Christopher (``Topher'') Eliot, Michael Lijewski, Pat Rankin, Miriam Robbins, -and Michal Jaegermann. Robert J. Chassell provided much valuable advice on -the use of Texinfo. - -Finally, we would like to thank Brian Kernighan of Bell Labs for invaluable -assistance during the testing and debugging of @code{gawk}, and for -help in clarifying numerous points about the language.@refill - -@node Copying, This Manual, Preface, Top -@unnumbered GNU GENERAL PUBLIC LICENSE -@center Version 2, June 1991 - -@display -Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. -675 Mass Ave, Cambridge, MA 02139, USA - -Everyone is permitted to copy and distribute verbatim copies -of this license document, but changing it is not allowed. -@end display - -@c fakenode --- for prepinfo -@unnumberedsec Preamble - - The licenses for most software are designed to take away your -freedom to share and change it. By contrast, the GNU General Public -License is intended to guarantee your freedom to share and change free -software---to make sure the software is free for all its users. This -General Public License applies to most of the Free Software -Foundation's software and to any other program whose authors commit to -using it. (Some other Free Software Foundation software is covered by -the GNU Library General Public License instead.) You can apply it to -your programs, too. - - When we speak of free software, we are referring to freedom, not -price. Our General Public Licenses are designed to make sure that you -have the freedom to distribute copies of free software (and charge for -this service if you wish), that you receive source code or can get it -if you want it, that you can change the software or use pieces of it -in new free programs; and that you know you can do these things. - - To protect your rights, we need to make restrictions that forbid -anyone to deny you these rights or to ask you to surrender the rights. -These restrictions translate to certain responsibilities for you if you -distribute copies of the software, or if you modify it. - - For example, if you distribute copies of such a program, whether -gratis or for a fee, you must give the recipients all the rights that -you have. You must make sure that they, too, receive or can get the -source code. And you must show them these terms so they know their -rights. - - We protect your rights with two steps: (1) copyright the software, and -(2) offer you this license which gives you legal permission to copy, -distribute and/or modify the software. - - Also, for each author's protection and ours, we want to make certain -that everyone understands that there is no warranty for this free -software. If the software is modified by someone else and passed on, we -want its recipients to know that what they have is not the original, so -that any problems introduced by others will not reflect on the original -authors' reputations. - - Finally, any free program is threatened constantly by software -patents. We wish to avoid the danger that redistributors of a free -program will individually obtain patent licenses, in effect making the -program proprietary. To prevent this, we have made it clear that any -patent must be licensed for everyone's free use or not licensed at all. - - The precise terms and conditions for copying, distribution and -modification follow. - -@iftex -@c fakenode --- for prepinfo -@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION -@end iftex -@ifinfo -@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION -@end ifinfo - -@enumerate -@item -This License applies to any program or other work which contains -a notice placed by the copyright holder saying it may be distributed -under the terms of this General Public License. The ``Program'', below, -refers to any such program or work, and a ``work based on the Program'' -means either the Program or any derivative work under copyright law: -that is to say, a work containing the Program or a portion of it, -either verbatim or with modifications and/or translated into another -language. (Hereinafter, translation is included without limitation in -the term ``modification''.) Each licensee is addressed as ``you''. - -Activities other than copying, distribution and modification are not -covered by this License; they are outside its scope. 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It is safest -to attach them to the start of each source file to most effectively -convey the exclusion of warranty; and each file should have at least -the ``copyright'' line and a pointer to where the full notice is found. - -@smallexample -@var{one line to give the program's name and a brief idea of what it does.} -Copyright (C) 19@var{yy} @var{name of author} - -This program is free software; you can redistribute it and/or modify -it under the terms of the GNU General Public License as published by -the Free Software Foundation; either version 2 of the License, or -(at your option) any later version. - -This program is distributed in the hope that it will be useful, -but WITHOUT ANY WARRANTY; without even the implied warranty of -MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -GNU General Public License for more details. - -You should have received a copy of the GNU General Public License -along with this program; if not, write to the Free Software -Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. -@end smallexample - -Also add information on how to contact you by electronic and paper mail. - -If the program is interactive, make it output a short notice like this -when it starts in an interactive mode: - -@smallexample -Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author} -Gnomovision comes with ABSOLUTELY NO WARRANTY; for details -type `show w'. -This is free software, and you are welcome to redistribute it -under certain conditions; type `show c' for details. -@end smallexample - -The hypothetical commands @samp{show w} and @samp{show c} should show -the appropriate parts of the General Public License. Of course, the -commands you use may be called something other than @samp{show w} and -@samp{show c}; they could even be mouse-clicks or menu items---whatever -suits your program. - -You should also get your employer (if you work as a programmer) or your -school, if any, to sign a ``copyright disclaimer'' for the program, if -necessary. Here is a sample; alter the names: - -@smallexample -Yoyodyne, Inc., hereby disclaims all copyright interest in the program -`Gnomovision' (which makes passes at compilers) written by James Hacker. - -@var{signature of Ty Coon}, 1 April 1989 -Ty Coon, President of Vice -@end smallexample - -This General Public License does not permit incorporating your program into -proprietary programs. If your program is a subroutine library, you may -consider it more useful to permit linking proprietary applications with the -library. If this is what you want to do, use the GNU Library General -Public License instead of this License. - -@node This Manual, Getting Started, Copying, Top -@chapter Using this Manual -@cindex manual, using this -@cindex using this manual -@cindex language, @code{awk} -@cindex program, @code{awk} -@cindex @code{awk} language -@cindex @code{awk} program - -The term @code{awk} refers to a particular program, and to the language you -use to tell this program what to do. When we need to be careful, we call -the program ``the @code{awk} utility'' and the language ``the @code{awk} -language.'' The term @code{gawk} refers to a version of @code{awk} developed -as part the GNU project. The purpose of this manual is to explain -both the -@code{awk} language and how to run the @code{awk} utility.@refill - -While concentrating on the features of @code{gawk}, the manual will also -attempt to describe important differences between @code{gawk} and other -@code{awk} implementations. In particular, any features that are not -in the @sc{posix} standard for @code{awk} will be noted. @refill - -The term @dfn{@code{awk} program} refers to a program written by you in -the @code{awk} programming language.@refill - -@xref{Getting Started, ,Getting Started with @code{awk}}, for the bare -essentials you need to know to start using @code{awk}. - -Some useful ``one-liners'' are included to give you a feel for the -@code{awk} language (@pxref{One-liners, ,Useful ``One-liners''}). - -@ignore -@strong{I deleted four paragraphs here because they would confuse the -beginner more than help him. They mention terms such as ``field,'' -``pattern,'' ``action,'' ``built-in function'' which the beginner -doesn't know.} - -@strong{If you can find a way to introduce several of these concepts here, -enough to give the reader a map of what is to follow, that might -be useful. I'm not sure that can be done without taking up more -space than ought to be used here. There may be no way to win.} - -@strong{ADR: I'd like to tackle this in phase 2 of my editing.} -@end ignore - -A sample @code{awk} program has been provided for you -(@pxref{Sample Program}).@refill - -If you find terms that you aren't familiar with, try looking them -up in the glossary (@pxref{Glossary}).@refill - -The entire @code{awk} language is summarized for quick reference in -@ref{Gawk Summary, ,@code{gawk} Summary}. Look there if you just need -to refresh your memory about a particular feature.@refill - -Most of the time complete @code{awk} programs are used as examples, but in -some of the more advanced sections, only the part of the @code{awk} program -that illustrates the concept being described is shown.@refill - -@menu -* Sample Data Files:: Sample data files for use in the @code{awk} - programs illustrated in this manual. -@end menu - -@node Sample Data Files, , This Manual, This Manual -@section Data Files for the Examples - -@cindex input file, sample -@cindex sample input file -@cindex @file{BBS-list} file -Many of the examples in this manual take their input from two sample -data files. The first, called @file{BBS-list}, represents a list of -computer bulletin board systems together with information about those systems. -The second data file, called @file{inventory-shipped}, contains -information about shipments on a monthly basis. Each line of these -files is one @dfn{record}. - -In the file @file{BBS-list}, each record contains the name of a computer -bulletin board, its phone number, the board's baud rate, and a code for -the number of hours it is operational. An @samp{A} in the last column -means the board operates 24 hours a day. A @samp{B} in the last -column means the board operates evening and weekend hours, only. A -@samp{C} means the board operates only on weekends. - -@example -aardvark 555-5553 1200/300 B -alpo-net 555-3412 2400/1200/300 A -barfly 555-7685 1200/300 A -bites 555-1675 2400/1200/300 A -camelot 555-0542 300 C -core 555-2912 1200/300 C -fooey 555-1234 2400/1200/300 B -foot 555-6699 1200/300 B -macfoo 555-6480 1200/300 A -sdace 555-3430 2400/1200/300 A -sabafoo 555-2127 1200/300 C -@end example - -@cindex @file{inventory-shipped} file -The second data file, called @file{inventory-shipped}, represents -information about shipments during the year. -Each record contains the month of the year, the number -of green crates shipped, the number of red boxes shipped, the number of -orange bags shipped, and the number of blue packages shipped, -respectively. There are 16 entries, covering the 12 months of one year -and 4 months of the next year.@refill - -@example -Jan 13 25 15 115 -Feb 15 32 24 226 -Mar 15 24 34 228 -Apr 31 52 63 420 -May 16 34 29 208 -Jun 31 42 75 492 -Jul 24 34 67 436 -Aug 15 34 47 316 -Sep 13 55 37 277 -Oct 29 54 68 525 -Nov 20 87 82 577 -Dec 17 35 61 401 - -Jan 21 36 64 620 -Feb 26 58 80 652 -Mar 24 75 70 495 -Apr 21 70 74 514 -@end example - -@ifinfo -If you are reading this in GNU Emacs using Info, you can copy the regions -of text showing these sample files into your own test files. This way you -can try out the examples shown in the remainder of this document. You do -this by using the command @kbd{M-x write-region} to copy text from the Info -file into a file for use with @code{awk} -(@xref{Misc File Ops, , , emacs, GNU Emacs Manual}, -for more information). Using this information, create your own -@file{BBS-list} and @file{inventory-shipped} files, and practice what you -learn in this manual. -@end ifinfo - -@node Getting Started, Reading Files, This Manual, Top -@chapter Getting Started with @code{awk} -@cindex script, definition of -@cindex rule, definition of -@cindex program, definition of -@cindex basic function of @code{gawk} - -The basic function of @code{awk} is to search files for lines (or other -units of text) that contain certain patterns. When a line matches one -of the patterns, @code{awk} performs specified actions on that line. -@code{awk} keeps processing input lines in this way until the end of the -input file is reached.@refill - -When you run @code{awk}, you specify an @code{awk} @dfn{program} which -tells @code{awk} what to do. The program consists of a series of -@dfn{rules}. (It may also contain @dfn{function definitions}, but that -is an advanced feature, so we will ignore it for now. -@xref{User-defined, ,User-defined Functions}.) Each rule specifies one -pattern to search for, and one action to perform when that pattern is found. - -Syntactically, a rule consists of a pattern followed by an action. The -action is enclosed in curly braces to separate it from the pattern. -Rules are usually separated by newlines. Therefore, an @code{awk} -program looks like this: - -@example -@var{pattern} @{ @var{action} @} -@var{pattern} @{ @var{action} @} -@dots{} -@end example - -@menu -* Very Simple:: A very simple example. -* Two Rules:: A less simple one-line example with two rules. -* More Complex:: A more complex example. -* Running gawk:: How to run @code{gawk} programs; - includes command line syntax. -* Comments:: Adding documentation to @code{gawk} programs. -* Statements/Lines:: Subdividing or combining statements into lines. -* When:: When to use @code{gawk} and - when to use other things. -@end menu - -@node Very Simple, Two Rules, Getting Started, Getting Started -@section A Very Simple Example - -@cindex @samp{print $0} -The following command runs a simple @code{awk} program that searches the -input file @file{BBS-list} for the string of characters: @samp{foo}. (A -string of characters is usually called, a @dfn{string}. -The term @dfn{string} is perhaps based on similar usage in English, such -as ``a string of pearls,'' or, ``a string of cars in a train.'') - -@example -awk '/foo/ @{ print $0 @}' BBS-list -@end example - -@noindent -When lines containing @samp{foo} are found, they are printed, because -@w{@samp{print $0}} means print the current line. (Just @samp{print} by -itself means the same thing, so we could have written that -instead.) - -You will notice that slashes, @samp{/}, surround the string @samp{foo} -in the actual @code{awk} program. The slashes indicate that @samp{foo} -is a pattern to search for. This type of pattern is called a -@dfn{regular expression}, and is covered in more detail later -(@pxref{Regexp, ,Regular Expressions as Patterns}). There are -single-quotes around the @code{awk} program so that the shell won't -interpret any of it as special shell characters.@refill - -Here is what this program prints: - -@example -@group -fooey 555-1234 2400/1200/300 B -foot 555-6699 1200/300 B -macfoo 555-6480 1200/300 A -sabafoo 555-2127 1200/300 C -@end group -@end example - -@cindex action, default -@cindex pattern, default -@cindex default action -@cindex default pattern -In an @code{awk} rule, either the pattern or the action can be omitted, -but not both. If the pattern is omitted, then the action is performed -for @emph{every} input line. If the action is omitted, the default -action is to print all lines that match the pattern. - -Thus, we could leave out the action (the @code{print} statement and the curly -braces) in the above example, and the result would be the same: all -lines matching the pattern @samp{foo} would be printed. By comparison, -omitting the @code{print} statement but retaining the curly braces makes an -empty action that does nothing; then no lines would be printed. - -@node Two Rules, More Complex, Very Simple, Getting Started -@section An Example with Two Rules -@cindex how @code{awk} works - -The @code{awk} utility reads the input files one line at a -time. For each line, @code{awk} tries the patterns of each of the rules. -If several patterns match then several actions are run, in the order in -which they appear in the @code{awk} program. If no patterns match, then -no actions are run. - -After processing all the rules (perhaps none) that match the line, -@code{awk} reads the next line (however, -@pxref{Next Statement, ,The @code{next} Statement}). This continues -until the end of the file is reached.@refill - -For example, the @code{awk} program: - -@example -/12/ @{ print $0 @} -/21/ @{ print $0 @} -@end example - -@noindent -contains two rules. The first rule has the string @samp{12} as the -pattern and @samp{print $0} as the action. The second rule has the -string @samp{21} as the pattern and also has @samp{print $0} as the -action. Each rule's action is enclosed in its own pair of braces. - -This @code{awk} program prints every line that contains the string -@samp{12} @emph{or} the string @samp{21}. If a line contains both -strings, it is printed twice, once by each rule. - -If we run this program on our two sample data files, @file{BBS-list} and -@file{inventory-shipped}, as shown here: - -@example -awk '/12/ @{ print $0 @} - /21/ @{ print $0 @}' BBS-list inventory-shipped -@end example - -@noindent -we get the following output: - -@example -aardvark 555-5553 1200/300 B -alpo-net 555-3412 2400/1200/300 A -barfly 555-7685 1200/300 A -bites 555-1675 2400/1200/300 A -core 555-2912 1200/300 C -fooey 555-1234 2400/1200/300 B -foot 555-6699 1200/300 B -macfoo 555-6480 1200/300 A -sdace 555-3430 2400/1200/300 A -sabafoo 555-2127 1200/300 C -sabafoo 555-2127 1200/300 C -Jan 21 36 64 620 -Apr 21 70 74 514 -@end example - -@noindent -Note how the line in @file{BBS-list} beginning with @samp{sabafoo} -was printed twice, once for each rule. - -@node More Complex, Running gawk, Two Rules, Getting Started -@comment node-name, next, previous, up -@section A More Complex Example - -Here is an example to give you an idea of what typical @code{awk} -programs do. This example shows how @code{awk} can be used to -summarize, select, and rearrange the output of another utility. It uses -features that haven't been covered yet, so don't worry if you don't -understand all the details. - -@example -ls -l | awk '$5 == "Nov" @{ sum += $4 @} - END @{ print sum @}' -@end example - -This command prints the total number of bytes in all the files in the -current directory that were last modified in November (of any year). -(In the C shell you would need to type a semicolon and then a backslash -at the end of the first line; in a @sc{posix}-compliant shell, such as the -Bourne shell or the Bourne-Again shell, you can type the example as shown.) - -The @w{@samp{ls -l}} part of this example is a command that gives you a -listing of the files in a directory, including file size and date. -Its output looks like this:@refill - -@example --rw-r--r-- 1 close 1933 Nov 7 13:05 Makefile --rw-r--r-- 1 close 10809 Nov 7 13:03 gawk.h --rw-r--r-- 1 close 983 Apr 13 12:14 gawk.tab.h --rw-r--r-- 1 close 31869 Jun 15 12:20 gawk.y --rw-r--r-- 1 close 22414 Nov 7 13:03 gawk1.c --rw-r--r-- 1 close 37455 Nov 7 13:03 gawk2.c --rw-r--r-- 1 close 27511 Dec 9 13:07 gawk3.c --rw-r--r-- 1 close 7989 Nov 7 13:03 gawk4.c -@end example - -@noindent -The first field contains read-write permissions, the second field contains -the number of links to the file, and the third field identifies the owner of -the file. The fourth field contains the size of the file in bytes. The -fifth, sixth, and seventh fields contain the month, day, and time, -respectively, that the file was last modified. Finally, the eighth field -contains the name of the file. - -The @code{$5 == "Nov"} in our @code{awk} program is an expression that -tests whether the fifth field of the output from @w{@samp{ls -l}} -matches the string @samp{Nov}. Each time a line has the string -@samp{Nov} in its fifth field, the action @samp{@{ sum += $4 @}} is -performed. This adds the fourth field (the file size) to the variable -@code{sum}. As a result, when @code{awk} has finished reading all the -input lines, @code{sum} is the sum of the sizes of files whose -lines matched the pattern. (This works because @code{awk} variables -are automatically initialized to zero.)@refill - -After the last line of output from @code{ls} has been processed, the -@code{END} rule is executed, and the value of @code{sum} is -printed. In this example, the value of @code{sum} would be 80600.@refill - -These more advanced @code{awk} techniques are covered in later sections -(@pxref{Actions, ,Overview of Actions}). Before you can move on to more -advanced @code{awk} programming, you have to know how @code{awk} interprets -your input and displays your output. By manipulating fields and using -@code{print} statements, you can produce some very useful and spectacular -looking reports.@refill - -@node Running gawk, Comments, More Complex, Getting Started -@section How to Run @code{awk} Programs - -@ignore -Date: Mon, 26 Aug 91 09:48:10 +0200 -From: gatech!vsoc07.cern.ch!matheys (Jean-Pol Matheys (CERN - ECP Division)) -To: uunet.UU.NET!skeeve!arnold -Subject: RE: status check - -The introduction of Chapter 2 (i.e. before 2.1) should include -the whole of section 2.4 - it's better to tell people how to run awk programs -before giving any examples - -ADR --- he's right. but for now, don't do this because the rest of the -chapter would need some rewriting. -@end ignore - -@cindex command line formats -@cindex running @code{awk} programs -There are several ways to run an @code{awk} program. If the program is -short, it is easiest to include it in the command that runs @code{awk}, -like this: - -@example -awk '@var{program}' @var{input-file1} @var{input-file2} @dots{} -@end example - -@noindent -where @var{program} consists of a series of patterns and actions, as -described earlier. - -When the program is long, it is usually more convenient to put it in a file -and run it with a command like this: - -@example -awk -f @var{program-file} @var{input-file1} @var{input-file2} @dots{} -@end example - -@menu -* One-shot:: Running a short throw-away @code{awk} program. -* Read Terminal:: Using no input files (input from - terminal instead). -* Long:: Putting permanent @code{awk} programs in files. -* Executable Scripts:: Making self-contained @code{awk} programs. -@end menu - -@node One-shot, Read Terminal, Running gawk, Running gawk -@subsection One-shot Throw-away @code{awk} Programs - -Once you are familiar with @code{awk}, you will often type simple -programs at the moment you want to use them. Then you can write the -program as the first argument of the @code{awk} command, like this: - -@example -awk '@var{program}' @var{input-file1} @var{input-file2} @dots{} -@end example - -@noindent -where @var{program} consists of a series of @var{patterns} and -@var{actions}, as described earlier. - -@cindex single quotes, why needed -This command format instructs the shell to start @code{awk} and use the -@var{program} to process records in the input file(s). There are single -quotes around @var{program} so that the shell doesn't interpret any -@code{awk} characters as special shell characters. They also cause the -shell to treat all of @var{program} as a single argument for -@code{awk} and allow @var{program} to be more than one line long.@refill - -This format is also useful for running short or medium-sized @code{awk} -programs from shell scripts, because it avoids the need for a separate -file for the @code{awk} program. A self-contained shell script is more -reliable since there are no other files to misplace. - -@node Read Terminal, Long, One-shot, Running gawk -@subsection Running @code{awk} without Input Files - -@cindex standard input -@cindex input, standard -You can also run @code{awk} without any input files. If you type the -command line:@refill - -@example -awk '@var{program}' -@end example - -@noindent -then @code{awk} applies the @var{program} to the @dfn{standard input}, -which usually means whatever you type on the terminal. This continues -until you indicate end-of-file by typing @kbd{Control-d}. - -For example, if you execute this command: - -@example -awk '/th/' -@end example - -@noindent -whatever you type next is taken as data for that @code{awk} -program. If you go on to type the following data: - -@example -Kathy -Ben -Tom -Beth -Seth -Karen -Thomas -@kbd{Control-d} -@end example - -@noindent -then @code{awk} prints this output: - -@example -Kathy -Beth -Seth -@end example - -@noindent -@cindex case sensitivity -@cindex pattern, case sensitive -as matching the pattern @samp{th}. Notice that it did not recognize -@samp{Thomas} as matching the pattern. The @code{awk} language is -@dfn{case sensitive}, and matches patterns exactly. (However, you can -override this with the variable @code{IGNORECASE}. -@xref{Case-sensitivity, ,Case-sensitivity in Matching}.) - -@node Long, Executable Scripts, Read Terminal, Running gawk -@subsection Running Long Programs - -@cindex running long programs -@cindex @samp{-f} option -@cindex program file -@cindex file, @code{awk} program -Sometimes your @code{awk} programs can be very long. In this case it is -more convenient to put the program into a separate file. To tell -@code{awk} to use that file for its program, you type:@refill - -@example -awk -f @var{source-file} @var{input-file1} @var{input-file2} @dots{} -@end example - -The @samp{-f} instructs the @code{awk} utility to get the @code{awk} program -from the file @var{source-file}. Any file name can be used for -@var{source-file}. For example, you could put the program:@refill - -@example -/th/ -@end example - -@noindent -into the file @file{th-prog}. Then this command: - -@example -awk -f th-prog -@end example - -@noindent -does the same thing as this one: - -@example -awk '/th/' -@end example - -@noindent -which was explained earlier (@pxref{Read Terminal, ,Running @code{awk} without Input Files}). -Note that you don't usually need single quotes around the file name that you -specify with @samp{-f}, because most file names don't contain any of the shell's -special characters. Notice that in @file{th-prog}, the @code{awk} -program did not have single quotes around it. The quotes are only needed -for programs that are provided on the @code{awk} command line. - -If you want to identify your @code{awk} program files clearly as such, -you can add the extension @file{.awk} to the file name. This doesn't -affect the execution of the @code{awk} program, but it does make -``housekeeping'' easier. - -@node Executable Scripts, , Long, Running gawk -@c node-name, next, previous, up -@subsection Executable @code{awk} Programs -@cindex executable scripts -@cindex scripts, executable -@cindex self contained programs -@cindex program, self contained -@cindex @samp{#!} - -Once you have learned @code{awk}, you may want to write self-contained -@code{awk} scripts, using the @samp{#!} script mechanism. You can do -this on many Unix systems @footnote{The @samp{#!} mechanism works on -Unix systems derived from Berkeley Unix, System V Release 4, and some System -V Release 3 systems.} (and someday on GNU).@refill - -For example, you could create a text file named @file{hello}, containing -the following (where @samp{BEGIN} is a feature we have not yet -discussed): - -@example -#! /bin/awk -f - -# a sample awk program -BEGIN @{ print "hello, world" @} -@end example - -@noindent -After making this file executable (with the @code{chmod} command), you -can simply type: - -@example -hello -@end example - -@noindent -at the shell, and the system will arrange to run @code{awk} @footnote{The -line beginning with @samp{#!} lists the full pathname of an interpreter -to be run, and an optional initial command line argument to pass to that -interpreter. The operating system then runs the interpreter with the given -argument and the full argument list of the executed program. The first argument -in the list is the full pathname of the @code{awk} program. The rest of the -argument list will either be options to @code{awk}, or data files, -or both.} as if you had typed:@refill - -@example -awk -f hello -@end example - -@noindent -Self-contained @code{awk} scripts are useful when you want to write a -program which users can invoke without knowing that the program is -written in @code{awk}. - -@cindex shell scripts -@cindex scripts, shell -If your system does not support the @samp{#!} mechanism, you can get a -similar effect using a regular shell script. It would look something -like this: - -@example -: The colon makes sure this script is executed by the Bourne shell. -awk '@var{program}' "$@@" -@end example - -Using this technique, it is @emph{vital} to enclose the @var{program} in -single quotes to protect it from interpretation by the shell. If you -omit the quotes, only a shell wizard can predict the results. - -The @samp{"$@@"} causes the shell to forward all the command line -arguments to the @code{awk} program, without interpretation. The first -line, which starts with a colon, is used so that this shell script will -work even if invoked by a user who uses the C shell. -@c Someday: (See @cite{The Bourne Again Shell}, by ??.) - -@node Comments, Statements/Lines, Running gawk, Getting Started -@section Comments in @code{awk} Programs -@cindex @samp{#} -@cindex comments -@cindex use of comments -@cindex documenting @code{awk} programs -@cindex programs, documenting - -A @dfn{comment} is some text that is included in a program for the sake -of human readers, and that is not really part of the program. Comments -can explain what the program does, and how it works. Nearly all -programming languages have provisions for comments, because programs are -typically hard to understand without their extra help. - -In the @code{awk} language, a comment starts with the sharp sign -character, @samp{#}, and continues to the end of the line. The -@code{awk} language ignores the rest of a line following a sharp sign. -For example, we could have put the following into @file{th-prog}:@refill - -@smallexample -# This program finds records containing the pattern @samp{th}. This is how -# you continue comments on additional lines. -/th/ -@end smallexample - -You can put comment lines into keyboard-composed throw-away @code{awk} -programs also, but this usually isn't very useful; the purpose of a -comment is to help you or another person understand the program at -a later time.@refill - -@node Statements/Lines, When, Comments, Getting Started -@section @code{awk} Statements versus Lines - -Most often, each line in an @code{awk} program is a separate statement or -separate rule, like this: - -@example -awk '/12/ @{ print $0 @} - /21/ @{ print $0 @}' BBS-list inventory-shipped -@end example - -But sometimes statements can be more than one line, and lines can -contain several statements. You can split a statement into multiple -lines by inserting a newline after any of the following:@refill - -@example -, @{ ? : || && do else -@end example - -@noindent -A newline at any other point is considered the end of the statement. -(Splitting lines after @samp{?} and @samp{:} is a minor @code{gawk} -extension. The @samp{?} and @samp{:} referred to here is the -three operand conditional expression described in -@ref{Conditional Exp, ,Conditional Expressions}.)@refill - -@cindex backslash continuation -@cindex continuation of lines -If you would like to split a single statement into two lines at a point -where a newline would terminate it, you can @dfn{continue} it by ending the -first line with a backslash character, @samp{\}. This is allowed -absolutely anywhere in the statement, even in the middle of a string or -regular expression. For example: - -@example -awk '/This program is too long, so continue it\ - on the next line/ @{ print $1 @}' -@end example - -@noindent -We have generally not used backslash continuation in the sample programs in -this manual. Since in @code{gawk} there is no limit on the length of a line, -it is never strictly necessary; it just makes programs prettier. We have -preferred to make them even more pretty by keeping the statements short. -Backslash continuation is most useful when your @code{awk} program is in a -separate source file, instead of typed in on the command line. You should -also note that many @code{awk} implementations are more picky about where -you may use backslash continuation. For maximal portability of your @code{awk} -programs, it is best not to split your lines in the middle of a regular -expression or a string.@refill - -@strong{Warning: backslash continuation does not work as described above -with the C shell.} Continuation with backslash works for @code{awk} -programs in files, and also for one-shot programs @emph{provided} you -are using a @sc{posix}-compliant shell, such as the Bourne shell or the -Bourne-again shell. But the C shell used on Berkeley Unix behaves -differently! There, you must use two backslashes in a row, followed by -a newline.@refill - -@cindex multiple statements on one line -When @code{awk} statements within one rule are short, you might want to put -more than one of them on a line. You do this by separating the statements -with a semicolon, @samp{;}. -This also applies to the rules themselves. -Thus, the previous program could have been written:@refill - -@example -/12/ @{ print $0 @} ; /21/ @{ print $0 @} -@end example - -@noindent -@strong{Note:} the requirement that rules on the same line must be -separated with a semicolon is a recent change in the @code{awk} -language; it was done for consistency with the treatment of statements -within an action. - -@node When, , Statements/Lines, Getting Started -@section When to Use @code{awk} - -@cindex when to use @code{awk} -@cindex applications of @code{awk} -You might wonder how @code{awk} might be useful for you. Using additional -utility programs, more advanced patterns, field separators, arithmetic -statements, and other selection criteria, you can produce much more -complex output. The @code{awk} language is very useful for producing -reports from large amounts of raw data, such as summarizing information -from the output of other utility programs like @code{ls}. -(@xref{More Complex, ,A More Complex Example}.) - -Programs written with @code{awk} are usually much smaller than they would -be in other languages. This makes @code{awk} programs easy to compose and -use. Often @code{awk} programs can be quickly composed at your terminal, -used once, and thrown away. Since @code{awk} programs are interpreted, you -can avoid the usually lengthy edit-compile-test-debug cycle of software -development. - -Complex programs have been written in @code{awk}, including a complete -retargetable assembler for 8-bit microprocessors (@pxref{Glossary}, for -more information) and a microcode assembler for a special purpose Prolog -computer. However, @code{awk}'s capabilities are strained by tasks of -such complexity. - -If you find yourself writing @code{awk} scripts of more than, say, a few -hundred lines, you might consider using a different programming -language. Emacs Lisp is a good choice if you need sophisticated string -or pattern matching capabilities. The shell is also good at string and -pattern matching; in addition, it allows powerful use of the system -utilities. More conventional languages, such as C, C++, and Lisp, offer -better facilities for system programming and for managing the complexity -of large programs. Programs in these languages may require more lines -of source code than the equivalent @code{awk} programs, but they are -easier to maintain and usually run more efficiently.@refill - -@node Reading Files, Printing, Getting Started, Top -@chapter Reading Input Files - -@cindex reading files -@cindex input -@cindex standard input -@vindex FILENAME -In the typical @code{awk} program, all input is read either from the -standard input (by default the keyboard, but often a pipe from another -command) or from files whose names you specify on the @code{awk} command -line. If you specify input files, @code{awk} reads them in order, reading -all the data from one before going on to the next. The name of the current -input file can be found in the built-in variable @code{FILENAME} -(@pxref{Built-in Variables}).@refill - -The input is read in units called records, and processed by the -rules one record at a time. By default, each record is one line. Each -record is split automatically into fields, to make it more -convenient for a rule to work on its parts. - -On rare occasions you will need to use the @code{getline} command, -which can do explicit input from any number of files -(@pxref{Getline, ,Explicit Input with @code{getline}}).@refill - -@menu -* Records:: Controlling how data is split into records. -* Fields:: An introduction to fields. -* Non-Constant Fields:: Non-constant Field Numbers. -* Changing Fields:: Changing the Contents of a Field. -* Field Separators:: The field separator and how to change it. -* Constant Size:: Reading constant width data. -* Multiple Line:: Reading multi-line records. -* Getline:: Reading files under explicit program control - using the @code{getline} function. -* Close Input:: Closing an input file (so you can read from - the beginning once more). -@end menu - -@node Records, Fields, Reading Files, Reading Files -@section How Input is Split into Records - -@cindex record separator -The @code{awk} language divides its input into records and fields. -Records are separated by a character called the @dfn{record separator}. -By default, the record separator is the newline character, defining -a record to be a single line of text.@refill - -@iftex -@cindex changing the record separator -@end iftex -@vindex RS -Sometimes you may want to use a different character to separate your -records. You can use a different character by changing the built-in -variable @code{RS}. The value of @code{RS} is a string that says how -to separate records; the default value is @code{"\n"}, the string containing -just a newline character. This is why records are, by default, single lines. - -@code{RS} can have any string as its value, but only the first character -of the string is used as the record separator. The other characters are -ignored. @code{RS} is exceptional in this regard; @code{awk} uses the -full value of all its other built-in variables.@refill - -@ignore -Someday this should be true! - -The value of @code{RS} is not limited to a one-character string. It can -be any regular expression (@pxref{Regexp, ,Regular Expressions as Patterns}). -In general, each record -ends at the next string that matches the regular expression; the next -record starts at the end of the matching string. This general rule is -actually at work in the usual case, where @code{RS} contains just a -newline: a record ends at the beginning of the next matching string (the -next newline in the input) and the following record starts just after -the end of this string (at the first character of the following line). -The newline, since it matches @code{RS}, is not part of either record.@refill -@end ignore - -You can change the value of @code{RS} in the @code{awk} program with the -assignment operator, @samp{=} (@pxref{Assignment Ops, ,Assignment Expressions}). -The new record-separator character should be enclosed in quotation marks to make -a string constant. Often the right time to do this is at the beginning -of execution, before any input has been processed, so that the very -first record will be read with the proper separator. To do this, use -the special @code{BEGIN} pattern -(@pxref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}). For -example:@refill - -@example -awk 'BEGIN @{ RS = "/" @} ; @{ print $0 @}' BBS-list -@end example - -@noindent -changes the value of @code{RS} to @code{"/"}, before reading any input. -This is a string whose first character is a slash; as a result, records -are separated by slashes. Then the input file is read, and the second -rule in the @code{awk} program (the action with no pattern) prints each -record. Since each @code{print} statement adds a newline at the end of -its output, the effect of this @code{awk} program is to copy the input -with each slash changed to a newline. - -Another way to change the record separator is on the command line, -using the variable-assignment feature -(@pxref{Command Line, ,Invoking @code{awk}}).@refill - -@example -awk '@{ print $0 @}' RS="/" BBS-list -@end example - -@noindent -This sets @code{RS} to @samp{/} before processing @file{BBS-list}. - -Reaching the end of an input file terminates the current input record, -even if the last character in the file is not the character in @code{RS}. - -@ignore -@c merge the preceding paragraph and this stuff into one paragraph -@c and put it in an `expert info' section. -This produces correct behavior in the vast majority of cases, although -the following (extreme) pipeline prints a surprising @samp{1}. (There -is one field, consisting of a newline.) - -@example -echo | awk 'BEGIN @{ RS = "a" @} ; @{ print NF @}' -@end example - -@end ignore - -The empty string, @code{""} (a string of no characters), has a special meaning -as the value of @code{RS}: it means that records are separated only -by blank lines. @xref{Multiple Line, ,Multiple-Line Records}, for more details. - -@cindex number of records, @code{NR} or @code{FNR} -@vindex NR -@vindex FNR -The @code{awk} utility keeps track of the number of records that have -been read so far from the current input file. This value is stored in a -built-in variable called @code{FNR}. It is reset to zero when a new -file is started. Another built-in variable, @code{NR}, is the total -number of input records read so far from all files. It starts at zero -but is never automatically reset to zero. - -If you change the value of @code{RS} in the middle of an @code{awk} run, -the new value is used to delimit subsequent records, but the record -currently being processed (and records already processed) are not -affected. - -@node Fields, Non-Constant Fields, Records, Reading Files -@section Examining Fields - -@cindex examining fields -@cindex fields -@cindex accessing fields -When @code{awk} reads an input record, the record is -automatically separated or @dfn{parsed} by the interpreter into chunks -called @dfn{fields}. By default, fields are separated by whitespace, -like words in a line. -Whitespace in @code{awk} means any string of one or more spaces and/or -tabs; other characters such as newline, formfeed, and so on, that are -considered whitespace by other languages are @emph{not} considered -whitespace by @code{awk}.@refill - -The purpose of fields is to make it more convenient for you to refer to -these pieces of the record. You don't have to use them---you can -operate on the whole record if you wish---but fields are what make -simple @code{awk} programs so powerful. - -@cindex @code{$} (field operator) -@cindex operators, @code{$} -To refer to a field in an @code{awk} program, you use a dollar-sign, -@samp{$}, followed by the number of the field you want. Thus, @code{$1} -refers to the first field, @code{$2} to the second, and so on. For -example, suppose the following is a line of input:@refill - -@example -This seems like a pretty nice example. -@end example - -@noindent -Here the first field, or @code{$1}, is @samp{This}; the second field, or -@code{$2}, is @samp{seems}; and so on. Note that the last field, -@code{$7}, is @samp{example.}. Because there is no space between the -@samp{e} and the @samp{.}, the period is considered part of the seventh -field.@refill - -No matter how many fields there are, the last field in a record can be -represented by @code{$NF}. So, in the example above, @code{$NF} would -be the same as @code{$7}, which is @samp{example.}. Why this works is -explained below (@pxref{Non-Constant Fields, ,Non-constant Field Numbers}). -If you try to refer to a field beyond the last one, such as @code{$8} -when the record has only 7 fields, you get the empty string.@refill - -@vindex NF -@cindex number of fields, @code{NF} -Plain @code{NF}, with no @samp{$}, is a built-in variable whose value -is the number of fields in the current record. - -@code{$0}, which looks like an attempt to refer to the zeroth field, is -a special case: it represents the whole input record. This is what you -would use if you weren't interested in fields. - -Here are some more examples: - -@example -awk '$1 ~ /foo/ @{ print $0 @}' BBS-list -@end example - -@noindent -This example prints each record in the file @file{BBS-list} whose first -field contains the string @samp{foo}. The operator @samp{~} is called a -@dfn{matching operator} (@pxref{Comparison Ops, ,Comparison Expressions}); -it tests whether a string (here, the field @code{$1}) matches a given regular -expression.@refill - -By contrast, the following example: - -@example -awk '/foo/ @{ print $1, $NF @}' BBS-list -@end example - -@noindent -looks for @samp{foo} in @emph{the entire record} and prints the first -field and the last field for each input record containing a -match.@refill - -@node Non-Constant Fields, Changing Fields, Fields, Reading Files -@section Non-constant Field Numbers - -The number of a field does not need to be a constant. Any expression in -the @code{awk} language can be used after a @samp{$} to refer to a -field. The value of the expression specifies the field number. If the -value is a string, rather than a number, it is converted to a number. -Consider this example:@refill - -@example -awk '@{ print $NR @}' -@end example - -@noindent -Recall that @code{NR} is the number of records read so far: 1 in the -first record, 2 in the second, etc. So this example prints the first -field of the first record, the second field of the second record, and so -on. For the twentieth record, field number 20 is printed; most likely, -the record has fewer than 20 fields, so this prints a blank line. - -Here is another example of using expressions as field numbers: - -@example -awk '@{ print $(2*2) @}' BBS-list -@end example - -The @code{awk} language must evaluate the expression @code{(2*2)} and use -its value as the number of the field to print. The @samp{*} sign -represents multiplication, so the expression @code{2*2} evaluates to 4. -The parentheses are used so that the multiplication is done before the -@samp{$} operation; they are necessary whenever there is a binary -operator in the field-number expression. This example, then, prints the -hours of operation (the fourth field) for every line of the file -@file{BBS-list}.@refill - -If the field number you compute is zero, you get the entire record. -Thus, @code{$(2-2)} has the same value as @code{$0}. Negative field -numbers are not allowed. - -The number of fields in the current record is stored in the built-in -variable @code{NF} (@pxref{Built-in Variables}). The expression -@code{$NF} is not a special feature: it is the direct consequence of -evaluating @code{NF} and using its value as a field number. - -@node Changing Fields, Field Separators, Non-Constant Fields, Reading Files -@section Changing the Contents of a Field - -@cindex field, changing contents of -@cindex changing contents of a field -@cindex assignment to fields -You can change the contents of a field as seen by @code{awk} within an -@code{awk} program; this changes what @code{awk} perceives as the -current input record. (The actual input is untouched: @code{awk} never -modifies the input file.) - -Consider this example: - -@smallexample -awk '@{ $3 = $2 - 10; print $2, $3 @}' inventory-shipped -@end smallexample - -@noindent -The @samp{-} sign represents subtraction, so this program reassigns -field three, @code{$3}, to be the value of field two minus ten, -@code{$2 - 10}. (@xref{Arithmetic Ops, ,Arithmetic Operators}.) -Then field two, and the new value for field three, are printed. - -In order for this to work, the text in field @code{$2} must make sense -as a number; the string of characters must be converted to a number in -order for the computer to do arithmetic on it. The number resulting -from the subtraction is converted back to a string of characters which -then becomes field three. -@xref{Conversion, ,Conversion of Strings and Numbers}.@refill - -When you change the value of a field (as perceived by @code{awk}), the -text of the input record is recalculated to contain the new field where -the old one was. Therefore, @code{$0} changes to reflect the altered -field. Thus, - -@smallexample -awk '@{ $2 = $2 - 10; print $0 @}' inventory-shipped -@end smallexample - -@noindent -prints a copy of the input file, with 10 subtracted from the second -field of each line. - -You can also assign contents to fields that are out of range. For -example: - -@smallexample -awk '@{ $6 = ($5 + $4 + $3 + $2) ; print $6 @}' inventory-shipped -@end smallexample - -@noindent -We've just created @code{$6}, whose value is the sum of fields -@code{$2}, @code{$3}, @code{$4}, and @code{$5}. The @samp{+} sign -represents addition. For the file @file{inventory-shipped}, @code{$6} -represents the total number of parcels shipped for a particular month. - -Creating a new field changes the internal @code{awk} copy of the current -input record---the value of @code{$0}. Thus, if you do @samp{print $0} -after adding a field, the record printed includes the new field, with -the appropriate number of field separators between it and the previously -existing fields. - -This recomputation affects and is affected by several features not yet -discussed, in particular, the @dfn{output field separator}, @code{OFS}, -which is used to separate the fields (@pxref{Output Separators}), and -@code{NF} (the number of fields; @pxref{Fields, ,Examining Fields}). -For example, the value of @code{NF} is set to the number of the highest -field you create.@refill - -Note, however, that merely @emph{referencing} an out-of-range field -does @emph{not} change the value of either @code{$0} or @code{NF}. -Referencing an out-of-range field merely produces a null string. For -example:@refill - -@smallexample -if ($(NF+1) != "") - print "can't happen" -else - print "everything is normal" -@end smallexample - -@noindent -should print @samp{everything is normal}, because @code{NF+1} is certain -to be out of range. (@xref{If Statement, ,The @code{if} Statement}, -for more information about @code{awk}'s @code{if-else} statements.)@refill - -It is important to note that assigning to a field will change the -value of @code{$0}, but will not change the value of @code{NF}, -even when you assign the null string to a field. For example: - -@smallexample -echo a b c d | awk '@{ OFS = ":"; $2 = "" ; print ; print NF @}' -@end smallexample - -@noindent -prints - -@smallexample -a::c:d -4 -@end smallexample - -@noindent -The field is still there, it just has an empty value. You can tell -because there are two colons in a row. - -@node Field Separators, Constant Size, Changing Fields, Reading Files -@section Specifying how Fields are Separated -@vindex FS -@cindex fields, separating -@cindex field separator, @code{FS} -@cindex @samp{-F} option - -(This section is rather long; it describes one of the most fundamental -operations in @code{awk}. If you are a novice with @code{awk}, we -recommend that you re-read this section after you have studied the -section on regular expressions, @ref{Regexp, ,Regular Expressions as Patterns}.) - -The way @code{awk} splits an input record into fields is controlled by -the @dfn{field separator}, which is a single character or a regular -expression. @code{awk} scans the input record for matches for the -separator; the fields themselves are the text between the matches. For -example, if the field separator is @samp{oo}, then the following line: - -@smallexample -moo goo gai pan -@end smallexample - -@noindent -would be split into three fields: @samp{m}, @samp{@ g} and @samp{@ gai@ -pan}. - -The field separator is represented by the built-in variable @code{FS}. -Shell programmers take note! @code{awk} does not use the name @code{IFS} -which is used by the shell.@refill - -You can change the value of @code{FS} in the @code{awk} program with the -assignment operator, @samp{=} (@pxref{Assignment Ops, ,Assignment Expressions}). -Often the right time to do this is at the beginning of execution, -before any input has been processed, so that the very first record -will be read with the proper separator. To do this, use the special -@code{BEGIN} pattern -(@pxref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}). -For example, here we set the value of @code{FS} to the string -@code{","}:@refill - -@smallexample -awk 'BEGIN @{ FS = "," @} ; @{ print $2 @}' -@end smallexample - -@noindent -Given the input line, - -@smallexample -John Q. Smith, 29 Oak St., Walamazoo, MI 42139 -@end smallexample - -@noindent -this @code{awk} program extracts the string @samp{@ 29 Oak St.}. - -@cindex field separator, choice of -@cindex regular expressions as field separators -Sometimes your input data will contain separator characters that don't -separate fields the way you thought they would. For instance, the -person's name in the example we've been using might have a title or -suffix attached, such as @samp{John Q. Smith, LXIX}. From input -containing such a name: - -@smallexample -John Q. Smith, LXIX, 29 Oak St., Walamazoo, MI 42139 -@end smallexample - -@noindent -the previous sample program would extract @samp{@ LXIX}, instead of -@samp{@ 29 Oak St.}. If you were expecting the program to print the -address, you would be surprised. So choose your data layout and -separator characters carefully to prevent such problems. - -As you know, by default, fields are separated by whitespace sequences -(spaces and tabs), not by single spaces: two spaces in a row do not -delimit an empty field. The default value of the field separator is a -string @w{@code{" "}} containing a single space. If this value were -interpreted in the usual way, each space character would separate -fields, so two spaces in a row would make an empty field between them. -The reason this does not happen is that a single space as the value of -@code{FS} is a special case: it is taken to specify the default manner -of delimiting fields. - -If @code{FS} is any other single character, such as @code{","}, then -each occurrence of that character separates two fields. Two consecutive -occurrences delimit an empty field. If the character occurs at the -beginning or the end of the line, that too delimits an empty field. The -space character is the only single character which does not follow these -rules. - -More generally, the value of @code{FS} may be a string containing any -regular expression. Then each match in the record for the regular -expression separates fields. For example, the assignment:@refill - -@smallexample -FS = ", \t" -@end smallexample - -@noindent -makes every area of an input line that consists of a comma followed by a -space and a tab, into a field separator. (@samp{\t} stands for a -tab.)@refill - -For a less trivial example of a regular expression, suppose you want -single spaces to separate fields the way single commas were used above. -You can set @code{FS} to @w{@code{"[@ ]"}}. This regular expression -matches a single space and nothing else. - -@c the following index entry is an overfull hbox. --mew 30jan1992 -@cindex field separator: on command line -@cindex command line, setting @code{FS} on -@code{FS} can be set on the command line. You use the @samp{-F} argument to -do so. For example: - -@smallexample -awk -F, '@var{program}' @var{input-files} -@end smallexample - -@noindent -sets @code{FS} to be the @samp{,} character. Notice that the argument uses -a capital @samp{F}. Contrast this with @samp{-f}, which specifies a file -containing an @code{awk} program. Case is significant in command options: -the @samp{-F} and @samp{-f} options have nothing to do with each other. -You can use both options at the same time to set the @code{FS} argument -@emph{and} get an @code{awk} program from a file.@refill - -@c begin expert info -The value used for the argument to @samp{-F} is processed in exactly the -same way as assignments to the built-in variable @code{FS}. This means that -if the field separator contains special characters, they must be escaped -appropriately. For example, to use a @samp{\} as the field separator, you -would have to type: - -@smallexample -# same as FS = "\\" -awk -F\\\\ '@dots{}' files @dots{} -@end smallexample - -@noindent -Since @samp{\} is used for quoting in the shell, @code{awk} will see -@samp{-F\\}. Then @code{awk} processes the @samp{\\} for escape -characters (@pxref{Constants, ,Constant Expressions}), finally yielding -a single @samp{\} to be used for the field separator. -@c end expert info - -As a special case, in compatibility mode -(@pxref{Command Line, ,Invoking @code{awk}}), if the -argument to @samp{-F} is @samp{t}, then @code{FS} is set to the tab -character. (This is because if you type @samp{-F\t}, without the quotes, -at the shell, the @samp{\} gets deleted, so @code{awk} figures that you -really want your fields to be separated with tabs, and not @samp{t}s. -Use @samp{-v FS="t"} on the command line if you really do want to separate -your fields with @samp{t}s.)@refill - -For example, let's use an @code{awk} program file called @file{baud.awk} -that contains the pattern @code{/300/}, and the action @samp{print $1}. -Here is the program: - -@smallexample -/300/ @{ print $1 @} -@end smallexample - -Let's also set @code{FS} to be the @samp{-} character, and run the -program on the file @file{BBS-list}. The following command prints a -list of the names of the bulletin boards that operate at 300 baud and -the first three digits of their phone numbers:@refill - -@smallexample -awk -F- -f baud.awk BBS-list -@end smallexample - -@noindent -It produces this output: - -@smallexample -aardvark 555 -alpo -barfly 555 -bites 555 -camelot 555 -core 555 -fooey 555 -foot 555 -macfoo 555 -sdace 555 -sabafoo 555 -@end smallexample - -@noindent -Note the second line of output. If you check the original file, you will -see that the second line looked like this: - -@smallexample -alpo-net 555-3412 2400/1200/300 A -@end smallexample - -The @samp{-} as part of the system's name was used as the field -separator, instead of the @samp{-} in the phone number that was -originally intended. This demonstrates why you have to be careful in -choosing your field and record separators. - -The following program searches the system password file, and prints -the entries for users who have no password: - -@smallexample -awk -F: '$2 == ""' /etc/passwd -@end smallexample - -@noindent -Here we use the @samp{-F} option on the command line to set the field -separator. Note that fields in @file{/etc/passwd} are separated by -colons. The second field represents a user's encrypted password, but if -the field is empty, that user has no password. - -@c begin expert info -According to the @sc{posix} standard, @code{awk} is supposed to behave -as if each record is split into fields at the time that it is read. -In particular, this means that you can change the value of @code{FS} -after a record is read, but before any of the fields are referenced. -The value of the fields (i.e. how they were split) should reflect the -old value of @code{FS}, not the new one. - -However, many implementations of @code{awk} do not do this. Instead, -they defer splitting the fields until a field reference actually happens, -using the @emph{current} value of @code{FS}! This behavior can be difficult -to diagnose. The following example illustrates the results of the two methods. -(The @code{sed} command prints just the first line of @file{/etc/passwd}.) - -@smallexample -sed 1q /etc/passwd | awk '@{ FS = ":" ; print $1 @}' -@end smallexample - -@noindent -will usually print - -@smallexample -root -@end smallexample - -@noindent -on an incorrect implementation of @code{awk}, while @code{gawk} -will print something like - -@smallexample -root:nSijPlPhZZwgE:0:0:Root:/: -@end smallexample -@c end expert info - -@c begin expert info -There is an important difference between the two cases of @samp{FS = @w{" "}} -(a single blank) and @samp{FS = @w{"[ \t]+"}} (which is a regular expression -matching one or more blanks or tabs). For both values of @code{FS}, fields -are separated by runs of blanks and/or tabs. However, when the value of -@code{FS} is @code{" "}, @code{awk} will strip leading and trailing whitespace -from the record, and then decide where the fields are. - -For example, the following expression prints @samp{b}: - -@smallexample -echo ' a b c d ' | awk '@{ print $2 @}' -@end smallexample - -@noindent -However, the following prints @samp{a}: - -@smallexample -echo ' a b c d ' | awk 'BEGIN @{ FS = "[ \t]+" @} ; @{ print $2 @}' -@end smallexample - -@noindent -In this case, the first field is null. - -The stripping of leading and trailing whitespace also comes into -play whenever @code{$0} is recomputed. For instance, this pipeline - -@smallexample -echo ' a b c d' | awk '@{ print; $2 = $2; print @}' -@end smallexample - -@noindent -produces this output: - -@smallexample - a b c d -a b c d -@end smallexample - -@noindent -The first @code{print} statement prints the record as it was read, -with leading whitespace intact. The assignment to @code{$2} rebuilds -@code{$0} by concatenating @code{$1} through @code{$NF} together, -separated by the value of @code{OFS}. Since the leading whitespace -was ignored when finding @code{$1}, it is not part of the new @code{$0}. -Finally, the last @code{print} statement prints the new @code{$0}. -@c end expert info - -The following table summarizes how fields are split, based on the -value of @code{FS}. - -@table @code -@item FS == " " -Fields are separated by runs of whitespace. Leading and trailing -whitespace are ignored. This is the default. - -@item FS == @var{any single character} -Fields are separated by each occurrence of the character. Multiple -successive occurrences delimit empty fields, as do leading and -trailing occurrences. - -@item FS == @var{regexp} -Fields are separated by occurrences of characters that match @var{regexp}. -Leading and trailing matches of @var{regexp} delimit empty fields. -@end table - -@node Constant Size, Multiple Line, Field Separators, Reading Files -@section Reading Fixed-width Data - -(This section discusses an advanced, experimental feature. If you are -a novice @code{awk} user, you may wish to skip it on the first reading.) - -@code{gawk} 2.13 introduced a new facility for dealing with fixed-width fields -with no distinctive field separator. Data of this nature arises typically -in one of at least two ways: the input for old FORTRAN programs where -numbers are run together, and the output of programs that did not anticipate -the use of their output as input for other programs. - -An example of the latter is a table where all the columns are lined up by -the use of a variable number of spaces and @emph{empty fields are just -spaces}. Clearly, @code{awk}'s normal field splitting based on @code{FS} -will not work well in this case. (Although a portable @code{awk} program -can use a series of @code{substr} calls on @code{$0}, this is awkward and -inefficient for a large number of fields.)@refill - -The splitting of an input record into fixed-width fields is specified by -assigning a string containing space-separated numbers to the built-in -variable @code{FIELDWIDTHS}. Each number specifies the width of the field -@emph{including} columns between fields. If you want to ignore the columns -between fields, you can specify the width as a separate field that is -subsequently ignored. - -The following data is the output of the @code{w} utility. It is useful -to illustrate the use of @code{FIELDWIDTHS}. - -@smallexample - 10:06pm up 21 days, 14:04, 23 users -User tty login@ idle JCPU PCPU what -hzuo ttyV0 8:58pm 9 5 vi p24.tex -hzang ttyV3 6:37pm 50 -csh -eklye ttyV5 9:53pm 7 1 em thes.tex -dportein ttyV6 8:17pm 1:47 -csh -gierd ttyD3 10:00pm 1 elm -dave ttyD4 9:47pm 4 4 w -brent ttyp0 26Jun91 4:46 26:46 4:41 bash -dave ttyq4 26Jun9115days 46 46 wnewmail -@end smallexample - -The following program takes the above input, converts the idle time to -number of seconds and prints out the first two fields and the calculated -idle time. (This program uses a number of @code{awk} features that -haven't been introduced yet.)@refill - -@smallexample -BEGIN @{ FIELDWIDTHS = "9 6 10 6 7 7 35" @} -NR > 2 @{ - idle = $4 - sub(/^ */, "", idle) # strip leading spaces - if (idle == "") idle = 0 - if (idle ~ /:/) @{ split(idle, t, ":"); idle = t[1] * 60 + t[2] @} - if (idle ~ /days/) @{ idle *= 24 * 60 * 60 @} - - print $1, $2, idle -@} -@end smallexample - -Here is the result of running the program on the data: - -@smallexample -hzuo ttyV0 0 -hzang ttyV3 50 -eklye ttyV5 0 -dportein ttyV6 107 -gierd ttyD3 1 -dave ttyD4 0 -brent ttyp0 286 -dave ttyq4 1296000 -@end smallexample - -Another (possibly more practical) example of fixed-width input data -would be the input from a deck of balloting cards. In some parts of -the United States, voters make their choices by punching holes in computer -cards. These cards are then processed to count the votes for any particular -candidate or on any particular issue. Since a voter may choose not to -vote on some issue, any column on the card may be empty. An @code{awk} -program for processing such data could use the @code{FIELDWIDTHS} feature -to simplify reading the data.@refill - -@c of course, getting gawk to run on a system with card readers is -@c another story! - -This feature is still experimental, and will likely evolve over time. - -@node Multiple Line, Getline, Constant Size, Reading Files -@section Multiple-Line Records - -@cindex multiple line records -@cindex input, multiple line records -@cindex reading files, multiple line records -@cindex records, multiple line -In some data bases, a single line cannot conveniently hold all the -information in one entry. In such cases, you can use multi-line -records. - -The first step in doing this is to choose your data format: when records -are not defined as single lines, how do you want to define them? -What should separate records? - -One technique is to use an unusual character or string to separate -records. For example, you could use the formfeed character (written -@code{\f} in @code{awk}, as in C) to separate them, making each record -a page of the file. To do this, just set the variable @code{RS} to -@code{"\f"} (a string containing the formfeed character). Any -other character could equally well be used, as long as it won't be part -of the data in a record.@refill - -@ignore -Another technique is to have blank lines separate records. The string -@code{"^\n+"} is a regular expression that matches any sequence of -newlines starting at the beginning of a line---in other words, it -matches a sequence of blank lines. If you set @code{RS} to this string, -a record always ends at the first blank line encountered. In -addition, a regular expression always matches the longest possible -sequence when there is a choice. So the next record doesn't start until -the first nonblank line that follows---no matter how many blank lines -appear in a row, they are considered one record-separator. -@end ignore - -Another technique is to have blank lines separate records. By a special -dispensation, a null string as the value of @code{RS} indicates that -records are separated by one or more blank lines. If you set @code{RS} -to the null string, a record always ends at the first blank line -encountered. And the next record doesn't start until the first nonblank -line that follows---no matter how many blank lines appear in a row, they -are considered one record-separator. (End of file is also considered -a record separator.)@refill -@c !!! This use of `end of file' is confusing. Needs to be clarified. - -The second step is to separate the fields in the record. One way to do -this is to put each field on a separate line: to do this, just set the -variable @code{FS} to the string @code{"\n"}. (This simple regular -expression matches a single newline.) - -Another way to separate fields is to divide each of the lines into fields -in the normal manner. This happens by default as a result of a special -feature: when @code{RS} is set to the null string, the newline character -@emph{always} acts as a field separator. This is in addition to whatever -field separations result from @code{FS}. - -The original motivation for this special exception was probably so that -you get useful behavior in the default case (i.e., @w{@code{FS == " "}}). -This feature can be a problem if you really don't want the -newline character to separate fields, since there is no way to -prevent it. However, you can work around this by using the @code{split} -function to break up the record manually -(@pxref{String Functions, ,Built-in Functions for String Manipulation}).@refill - -@ignore -Here are two ways to use records separated by blank lines and break each -line into fields normally: - -@example -awk 'BEGIN @{ RS = ""; FS = "[ \t\n]+" @} @{ print $1 @}' BBS-list - -@exdent @r{or} - -awk 'BEGIN @{ RS = "^\n+"; FS = "[ \t\n]+" @} @{ print $1 @}' BBS-list -@end example -@end ignore - -@ignore -Here is how to use records separated by blank lines and break each -line into fields normally: - -@example -awk 'BEGIN @{ RS = ""; FS = "[ \t\n]+" @} ; @{ print $1 @}' BBS-list -@end example -@end ignore - -@node Getline, Close Input, Multiple Line, Reading Files -@section Explicit Input with @code{getline} - -@findex getline -@cindex input, explicit -@cindex explicit input -@cindex input, @code{getline} command -@cindex reading files, @code{getline} command -So far we have been getting our input files from @code{awk}'s main -input stream---either the standard input (usually your terminal) or the -files specified on the command line. The @code{awk} language has a -special built-in command called @code{getline} that -can be used to read input under your explicit control.@refill - -This command is quite complex and should @emph{not} be used by -beginners. It is covered here because this is the chapter on input. -The examples that follow the explanation of the @code{getline} command -include material that has not been covered yet. Therefore, come back -and study the @code{getline} command @emph{after} you have reviewed the -rest of this manual and have a good knowledge of how @code{awk} works. - -@vindex ERRNO -@cindex differences: @code{gawk} and @code{awk} -@code{getline} returns 1 if it finds a record, and 0 if the end of the -file is encountered. If there is some error in getting a record, such -as a file that cannot be opened, then @code{getline} returns @minus{}1. -In this case, @code{gawk} sets the variable @code{ERRNO} to a string -describing the error that occurred. - -In the following examples, @var{command} stands for a string value that -represents a shell command. - -@table @code -@item getline -The @code{getline} command can be used without arguments to read input -from the current input file. All it does in this case is read the next -input record and split it up into fields. This is useful if you've -finished processing the current record, but you want to do some special -processing @emph{right now} on the next record. Here's an -example:@refill - -@example -awk '@{ - if (t = index($0, "/*")) @{ - if (t > 1) - tmp = substr($0, 1, t - 1) - else - tmp = "" - u = index(substr($0, t + 2), "*/") - while (u == 0) @{ - getline - t = -1 - u = index($0, "*/") - @} - if (u <= length($0) - 2) - $0 = tmp substr($0, t + u + 3) - else - $0 = tmp - @} - print $0 -@}' -@end example - -This @code{awk} program deletes all C-style comments, @samp{/* @dots{} -*/}, from the input. By replacing the @samp{print $0} with other -statements, you could perform more complicated processing on the -decommented input, like searching for matches of a regular -expression. (This program has a subtle problem---can you spot it?) - -@c the program to remove comments doesn't work if one -@c comment ends and another begins on the same line. (Your -@c idea for restart would be useful here). --- brennan@boeing.com - -This form of the @code{getline} command sets @code{NF} (the number of -fields; @pxref{Fields, ,Examining Fields}), @code{NR} (the number of -records read so far; @pxref{Records, ,How Input is Split into Records}), -@code{FNR} (the number of records read from this input file), and the -value of @code{$0}. - -@strong{Note:} the new value of @code{$0} is used in testing -the patterns of any subsequent rules. The original value -of @code{$0} that triggered the rule which executed @code{getline} -is lost. By contrast, the @code{next} statement reads a new record -but immediately begins processing it normally, starting with the first -rule in the program. @xref{Next Statement, ,The @code{next} Statement}. - -@item getline @var{var} -This form of @code{getline} reads a record into the variable @var{var}. -This is useful when you want your program to read the next record from -the current input file, but you don't want to subject the record to the -normal input processing. - -For example, suppose the next line is a comment, or a special string, -and you want to read it, but you must make certain that it won't trigger -any rules. This version of @code{getline} allows you to read that line -and store it in a variable so that the main -read-a-line-and-check-each-rule loop of @code{awk} never sees it. - -The following example swaps every two lines of input. For example, given: - -@example -wan -tew -free -phore -@end example - -@noindent -it outputs: - -@example -tew -wan -phore -free -@end example - -@noindent -Here's the program: - -@example -@group -awk '@{ - if ((getline tmp) > 0) @{ - print tmp - print $0 - @} else - print $0 -@}' -@end group -@end example - -The @code{getline} function used in this way sets only the variables -@code{NR} and @code{FNR} (and of course, @var{var}). The record is not -split into fields, so the values of the fields (including @code{$0}) and -the value of @code{NF} do not change.@refill - -@item getline < @var{file} -@cindex input redirection -@cindex redirection of input -This form of the @code{getline} function takes its input from the file -@var{file}. Here @var{file} is a string-valued expression that -specifies the file name. @samp{< @var{file}} is called a @dfn{redirection} -since it directs input to come from a different place. - -This form is useful if you want to read your input from a particular -file, instead of from the main input stream. For example, the following -program reads its input record from the file @file{foo.input} when it -encounters a first field with a value equal to 10 in the current input -file.@refill - -@example -awk '@{ - if ($1 == 10) @{ - getline < "foo.input" - print - @} else - print -@}' -@end example - -Since the main input stream is not used, the values of @code{NR} and -@code{FNR} are not changed. But the record read is split into fields in -the normal manner, so the values of @code{$0} and other fields are -changed. So is the value of @code{NF}. - -This does not cause the record to be tested against all the patterns -in the @code{awk} program, in the way that would happen if the record -were read normally by the main processing loop of @code{awk}. However -the new record is tested against any subsequent rules, just as when -@code{getline} is used without a redirection. - -@item getline @var{var} < @var{file} -This form of the @code{getline} function takes its input from the file -@var{file} and puts it in the variable @var{var}. As above, @var{file} -is a string-valued expression that specifies the file from which to read. - -In this version of @code{getline}, none of the built-in variables are -changed, and the record is not split into fields. The only variable -changed is @var{var}. - -For example, the following program copies all the input files to the -output, except for records that say @w{@samp{@@include @var{filename}}}. -Such a record is replaced by the contents of the file -@var{filename}.@refill - -@example -awk '@{ - if (NF == 2 && $1 == "@@include") @{ - while ((getline line < $2) > 0) - print line - close($2) - @} else - print -@}' -@end example - -Note here how the name of the extra input file is not built into -the program; it is taken from the data, from the second field on -the @samp{@@include} line.@refill - -The @code{close} function is called to ensure that if two identical -@samp{@@include} lines appear in the input, the entire specified file is -included twice. @xref{Close Input, ,Closing Input Files and Pipes}.@refill - -One deficiency of this program is that it does not process nested -@samp{@@include} statements the way a true macro preprocessor would. - -@item @var{command} | getline -You can @dfn{pipe} the output of a command into @code{getline}. A pipe is -simply a way to link the output of one program to the input of another. In -this case, the string @var{command} is run as a shell command and its output -is piped into @code{awk} to be used as input. This form of @code{getline} -reads one record from the pipe. - -For example, the following program copies input to output, except for lines -that begin with @samp{@@execute}, which are replaced by the output produced by -running the rest of the line as a shell command: - -@example -awk '@{ - if ($1 == "@@execute") @{ - tmp = substr($0, 10) - while ((tmp | getline) > 0) - print - close(tmp) - @} else - print -@}' -@end example - -@noindent -The @code{close} function is called to ensure that if two identical -@samp{@@execute} lines appear in the input, the command is run for -each one. @xref{Close Input, ,Closing Input Files and Pipes}. - -Given the input: - -@example -foo -bar -baz -@@execute who -bletch -@end example - -@noindent -the program might produce: - -@example -foo -bar -baz -hack ttyv0 Jul 13 14:22 -hack ttyp0 Jul 13 14:23 (gnu:0) -hack ttyp1 Jul 13 14:23 (gnu:0) -hack ttyp2 Jul 13 14:23 (gnu:0) -hack ttyp3 Jul 13 14:23 (gnu:0) -bletch -@end example - -@noindent -Notice that this program ran the command @code{who} and printed the result. -(If you try this program yourself, you will get different results, showing -you who is logged in on your system.) - -This variation of @code{getline} splits the record into fields, sets the -value of @code{NF} and recomputes the value of @code{$0}. The values of -@code{NR} and @code{FNR} are not changed. - -@item @var{command} | getline @var{var} -The output of the command @var{command} is sent through a pipe to -@code{getline} and into the variable @var{var}. For example, the -following program reads the current date and time into the variable -@code{current_time}, using the @code{date} utility, and then -prints it.@refill - -@example -awk 'BEGIN @{ - "date" | getline current_time - close("date") - print "Report printed on " current_time -@}' -@end example - -In this version of @code{getline}, none of the built-in variables are -changed, and the record is not split into fields. -@end table - -@node Close Input, , Getline, Reading Files -@section Closing Input Files and Pipes -@cindex closing input files and pipes -@findex close - -If the same file name or the same shell command is used with -@code{getline} more than once during the execution of an @code{awk} -program, the file is opened (or the command is executed) only the first time. -At that time, the first record of input is read from that file or command. -The next time the same file or command is used in @code{getline}, another -record is read from it, and so on. - -This implies that if you want to start reading the same file again from -the beginning, or if you want to rerun a shell command (rather than -reading more output from the command), you must take special steps. -What you must do is use the @code{close} function, as follows: - -@example -close(@var{filename}) -@end example - -@noindent -or - -@example -close(@var{command}) -@end example - -The argument @var{filename} or @var{command} can be any expression. Its -value must exactly equal the string that was used to open the file or -start the command---for example, if you open a pipe with this: - -@example -"sort -r names" | getline foo -@end example - -@noindent -then you must close it with this: - -@example -close("sort -r names") -@end example - -Once this function call is executed, the next @code{getline} from that -file or command will reopen the file or rerun the command. - -@iftex -@vindex ERRNO -@cindex differences: @code{gawk} and @code{awk} -@end iftex -@code{close} returns a value of zero if the close succeeded. -Otherwise, the value will be non-zero. -In this case, @code{gawk} sets the variable @code{ERRNO} to a string -describing the error that occurred. - -@node Printing, One-liners, Reading Files, Top -@chapter Printing Output - -@cindex printing -@cindex output -One of the most common things that actions do is to output or @dfn{print} -some or all of the input. For simple output, use the @code{print} -statement. For fancier formatting use the @code{printf} statement. -Both are described in this chapter. - -@menu -* Print:: The @code{print} statement. -* Print Examples:: Simple examples of @code{print} statements. -* Output Separators:: The output separators and how to change them. -* OFMT:: Controlling Numeric Output With @code{print}. -* Printf:: The @code{printf} statement. -* Redirection:: How to redirect output to multiple - files and pipes. -* Special Files:: File name interpretation in @code{gawk}. - @code{gawk} allows access to - inherited file descriptors. -@end menu - -@node Print, Print Examples, Printing, Printing -@section The @code{print} Statement -@cindex @code{print} statement - -The @code{print} statement does output with simple, standardized -formatting. You specify only the strings or numbers to be printed, in a -list separated by commas. They are output, separated by single spaces, -followed by a newline. The statement looks like this: - -@example -print @var{item1}, @var{item2}, @dots{} -@end example - -@noindent -The entire list of items may optionally be enclosed in parentheses. The -parentheses are necessary if any of the item expressions uses a -relational operator; otherwise it could be confused with a redirection -(@pxref{Redirection, ,Redirecting Output of @code{print} and @code{printf}}). -The relational operators are @samp{==}, -@samp{!=}, @samp{<}, @samp{>}, @samp{>=}, @samp{<=}, @samp{~} and -@samp{!~} (@pxref{Comparison Ops, ,Comparison Expressions}).@refill - -The items printed can be constant strings or numbers, fields of the -current record (such as @code{$1}), variables, or any @code{awk} -expressions. The @code{print} statement is completely general for -computing @emph{what} values to print. With two exceptions, -you cannot specify @emph{how} to print them---how many -columns, whether to use exponential notation or not, and so on. -(@xref{Output Separators}, and -@ref{OFMT, ,Controlling Numeric Output with @code{print}}.) -For that, you need the @code{printf} statement -(@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}).@refill - -The simple statement @samp{print} with no items is equivalent to -@samp{print $0}: it prints the entire current record. To print a blank -line, use @samp{print ""}, where @code{""} is the null, or empty, -string. - -To print a fixed piece of text, use a string constant such as -@w{@code{"Hello there"}} as one item. If you forget to use the -double-quote characters, your text will be taken as an @code{awk} -expression, and you will probably get an error. Keep in mind that a -space is printed between any two items. - -Most often, each @code{print} statement makes one line of output. But it -isn't limited to one line. If an item value is a string that contains a -newline, the newline is output along with the rest of the string. A -single @code{print} can make any number of lines this way. - -@node Print Examples, Output Separators, Print, Printing -@section Examples of @code{print} Statements - -Here is an example of printing a string that contains embedded newlines: - -@example -awk 'BEGIN @{ print "line one\nline two\nline three" @}' -@end example - -@noindent -produces output like this: - -@example -line one -line two -line three -@end example - -Here is an example that prints the first two fields of each input record, -with a space between them: - -@example -awk '@{ print $1, $2 @}' inventory-shipped -@end example - -@noindent -Its output looks like this: - -@example -Jan 13 -Feb 15 -Mar 15 -@dots{} -@end example - -A common mistake in using the @code{print} statement is to omit the comma -between two items. This often has the effect of making the items run -together in the output, with no space. The reason for this is that -juxtaposing two string expressions in @code{awk} means to concatenate -them. For example, without the comma: - -@example -awk '@{ print $1 $2 @}' inventory-shipped -@end example - -@noindent -prints: - -@example -@group -Jan13 -Feb15 -Mar15 -@dots{} -@end group -@end example - -Neither example's output makes much sense to someone unfamiliar with the -file @file{inventory-shipped}. A heading line at the beginning would make -it clearer. Let's add some headings to our table of months (@code{$1}) and -green crates shipped (@code{$2}). We do this using the @code{BEGIN} pattern -(@pxref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}) to force the headings to be printed only once: - -@example -awk 'BEGIN @{ print "Month Crates" - print "----- ------" @} - @{ print $1, $2 @}' inventory-shipped -@end example - -@noindent -Did you already guess what happens? This program prints the following: - -@example -@group -Month Crates ------ ------ -Jan 13 -Feb 15 -Mar 15 -@dots{} -@end group -@end example - -@noindent -The headings and the table data don't line up! We can fix this by printing -some spaces between the two fields: - -@example -awk 'BEGIN @{ print "Month Crates" - print "----- ------" @} - @{ print $1, " ", $2 @}' inventory-shipped -@end example - -You can imagine that this way of lining up columns can get pretty -complicated when you have many columns to fix. Counting spaces for two -or three columns can be simple, but more than this and you can get -``lost'' quite easily. This is why the @code{printf} statement was -created (@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}); -one of its specialties is lining up columns of data.@refill - -@node Output Separators, OFMT, Print Examples, Printing -@section Output Separators - -@cindex output field separator, @code{OFS} -@vindex OFS -@vindex ORS -@cindex output record separator, @code{ORS} -As mentioned previously, a @code{print} statement contains a list -of items, separated by commas. In the output, the items are normally -separated by single spaces. But they do not have to be spaces; a -single space is only the default. You can specify any string of -characters to use as the @dfn{output field separator} by setting the -built-in variable @code{OFS}. The initial value of this variable -is the string @w{@code{" "}}, that is, just a single space.@refill - -The output from an entire @code{print} statement is called an -@dfn{output record}. Each @code{print} statement outputs one output -record and then outputs a string called the @dfn{output record separator}. -The built-in variable @code{ORS} specifies this string. The initial -value of the variable is the string @code{"\n"} containing a newline -character; thus, normally each @code{print} statement makes a separate line. - -You can change how output fields and records are separated by assigning -new values to the variables @code{OFS} and/or @code{ORS}. The usual -place to do this is in the @code{BEGIN} rule -(@pxref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}), so -that it happens before any input is processed. You may also do this -with assignments on the command line, before the names of your input -files.@refill - -The following example prints the first and second fields of each input -record separated by a semicolon, with a blank line added after each -line:@refill - -@example -@group -awk 'BEGIN @{ OFS = ";"; ORS = "\n\n" @} - @{ print $1, $2 @}' BBS-list -@end group -@end example - -If the value of @code{ORS} does not contain a newline, all your output -will be run together on a single line, unless you output newlines some -other way. - -@node OFMT, Printf, Output Separators, Printing -@section Controlling Numeric Output with @code{print} -@vindex OFMT -When you use the @code{print} statement to print numeric values, -@code{awk} internally converts the number to a string of characters, -and prints that string. @code{awk} uses the @code{sprintf} function -to do this conversion. For now, it suffices to say that the @code{sprintf} -function accepts a @dfn{format specification} that tells it how to format -numbers (or strings), and that there are a number of different ways that -numbers can be formatted. The different format specifications are discussed -more fully in -@ref{Printf, ,Using @code{printf} Statements for Fancier Printing}.@refill - -The built-in variable @code{OFMT} contains the default format specification -that @code{print} uses with @code{sprintf} when it wants to convert a -number to a string for printing. By supplying different format specifications -as the value of @code{OFMT}, you can change how @code{print} will print -your numbers. As a brief example: - -@example -@group -awk 'BEGIN @{ OFMT = "%d" # print numbers as integers - print 17.23 @}' -@end group -@end example - -@noindent -will print @samp{17}. - -@node Printf, Redirection, OFMT, Printing -@section Using @code{printf} Statements for Fancier Printing -@cindex formatted output -@cindex output, formatted - -If you want more precise control over the output format than -@code{print} gives you, use @code{printf}. With @code{printf} you can -specify the width to use for each item, and you can specify various -stylistic choices for numbers (such as what radix to use, whether to -print an exponent, whether to print a sign, and how many digits to print -after the decimal point). You do this by specifying a string, called -the @dfn{format string}, which controls how and where to print the other -arguments. - -@menu -* Basic Printf:: Syntax of the @code{printf} statement. -* Control Letters:: Format-control letters. -* Format Modifiers:: Format-specification modifiers. -* Printf Examples:: Several examples. -@end menu - -@node Basic Printf, Control Letters, Printf, Printf -@subsection Introduction to the @code{printf} Statement - -@cindex @code{printf} statement, syntax of -The @code{printf} statement looks like this:@refill - -@example -printf @var{format}, @var{item1}, @var{item2}, @dots{} -@end example - -@noindent -The entire list of arguments may optionally be enclosed in parentheses. The -parentheses are necessary if any of the item expressions uses a -relational operator; otherwise it could be confused with a redirection -(@pxref{Redirection, ,Redirecting Output of @code{print} and @code{printf}}). -The relational operators are @samp{==}, -@samp{!=}, @samp{<}, @samp{>}, @samp{>=}, @samp{<=}, @samp{~} and -@samp{!~} (@pxref{Comparison Ops, ,Comparison Expressions}).@refill - -@cindex format string -The difference between @code{printf} and @code{print} is the argument -@var{format}. This is an expression whose value is taken as a string; it -specifies how to output each of the other arguments. It is called -the @dfn{format string}. - -The format string is the same as in the @sc{ansi} C library function -@code{printf}. Most of @var{format} is text to be output verbatim. -Scattered among this text are @dfn{format specifiers}, one per item. -Each format specifier says to output the next item at that place in the -format.@refill - -The @code{printf} statement does not automatically append a newline to its -output. It outputs only what the format specifies. So if you want -a newline, you must include one in the format. The output separator -variables @code{OFS} and @code{ORS} have no effect on @code{printf} -statements.@refill - -@node Control Letters, Format Modifiers, Basic Printf, Printf -@subsection Format-Control Letters -@cindex @code{printf}, format-control characters -@cindex format specifier - -A format specifier starts with the character @samp{%} and ends with a -@dfn{format-control letter}; it tells the @code{printf} statement how -to output one item. (If you actually want to output a @samp{%}, write -@samp{%%}.) The format-control letter specifies what kind of value to -print. The rest of the format specifier is made up of optional -@dfn{modifiers} which are parameters such as the field width to use.@refill - -Here is a list of the format-control letters: - -@table @samp -@item c -This prints a number as an ASCII character. Thus, @samp{printf "%c", -65} outputs the letter @samp{A}. The output for a string value is -the first character of the string. - -@item d -This prints a decimal integer. - -@item i -This also prints a decimal integer. - -@item e -This prints a number in scientific (exponential) notation. -For example, - -@example -printf "%4.3e", 1950 -@end example - -@noindent -prints @samp{1.950e+03}, with a total of four significant figures of -which three follow the decimal point. The @samp{4.3} are @dfn{modifiers}, -discussed below. - -@item f -This prints a number in floating point notation. - -@item g -This prints a number in either scientific notation or floating point -notation, whichever uses fewer characters. -@ignore -From: gatech!ames!elroy!cit-vax!EQL.Caltech.Edu!rankin (Pat Rankin) - -In the description of printf formats (p.43), the information for %g -is incorrect (mainly, it's too much of an oversimplification). It's -wrong in the AWK book too, and in the gawk man page. I suggested to -David Trueman before 2.13 was released that the latter be revised, so -that it matched gawk's behavior (rather than trying to change gawk to -match the docs ;-). The documented description is nice and simple, but -it doesn't match the actual underlying behavior of %g in the various C -run-time libraries that gawk relies on. The precision value for g format -is different than for f and e formats, so it's inaccurate to say 'g' is -the shorter of 'e' or 'f'. For 'g', precision represents the number of -significant digits rather than the number of decimal places, and it has -special rules about how to format numbers with range between 10E-1 and -10E-4. All in all, it's pretty messy, and I had to add that clumsy -GFMT_WORKAROUND code because the VMS run-time library doesn't conform to -the ANSI-C specifications. -@end ignore - -@item o -This prints an unsigned octal integer. - -@item s -This prints a string. - -@item x -This prints an unsigned hexadecimal integer. - -@item X -This prints an unsigned hexadecimal integer. However, for the values 10 -through 15, it uses the letters @samp{A} through @samp{F} instead of -@samp{a} through @samp{f}. - -@item % -This isn't really a format-control letter, but it does have a meaning -when used after a @samp{%}: the sequence @samp{%%} outputs one -@samp{%}. It does not consume an argument. -@end table - -@node Format Modifiers, Printf Examples, Control Letters, Printf -@subsection Modifiers for @code{printf} Formats - -@cindex @code{printf}, modifiers -@cindex modifiers (in format specifiers) -A format specification can also include @dfn{modifiers} that can control -how much of the item's value is printed and how much space it gets. The -modifiers come between the @samp{%} and the format-control letter. Here -are the possible modifiers, in the order in which they may appear: - -@table @samp -@item - -The minus sign, used before the width modifier, says to left-justify -the argument within its specified width. Normally the argument -is printed right-justified in the specified width. Thus, - -@example -printf "%-4s", "foo" -@end example - -@noindent -prints @samp{foo }. - -@item @var{width} -This is a number representing the desired width of a field. Inserting any -number between the @samp{%} sign and the format control character forces the -field to be expanded to this width. The default way to do this is to -pad with spaces on the left. For example, - -@example -printf "%4s", "foo" -@end example - -@noindent -prints @samp{ foo}. - -The value of @var{width} is a minimum width, not a maximum. If the item -value requires more than @var{width} characters, it can be as wide as -necessary. Thus, - -@example -printf "%4s", "foobar" -@end example - -@noindent -prints @samp{foobar}. - -Preceding the @var{width} with a minus sign causes the output to be -padded with spaces on the right, instead of on the left. - -@item .@var{prec} -This is a number that specifies the precision to use when printing. -This specifies the number of digits you want printed to the right of the -decimal point. For a string, it specifies the maximum number of -characters from the string that should be printed. -@end table - -The C library @code{printf}'s dynamic @var{width} and @var{prec} -capability (for example, @code{"%*.*s"}) is supported. Instead of -supplying explicit @var{width} and/or @var{prec} values in the format -string, you pass them in the argument list. For example:@refill - -@example -w = 5 -p = 3 -s = "abcdefg" -printf "<%*.*s>\n", w, p, s -@end example - -@noindent -is exactly equivalent to - -@example -s = "abcdefg" -printf "<%5.3s>\n", s -@end example - -@noindent -Both programs output @samp{@w{<@bullet{}@bullet{}abc>}}. (We have -used the bullet symbol ``@bullet{}'' to represent a space, to clearly -show you that there are two spaces in the output.)@refill - -Earlier versions of @code{awk} did not support this capability. You may -simulate it by using concatenation to build up the format string, -like so:@refill - -@example -w = 5 -p = 3 -s = "abcdefg" -printf "<%" w "." p "s>\n", s -@end example - -@noindent -This is not particularly easy to read, however. - -@node Printf Examples, , Format Modifiers, Printf -@subsection Examples of Using @code{printf} - -Here is how to use @code{printf} to make an aligned table: - -@example -awk '@{ printf "%-10s %s\n", $1, $2 @}' BBS-list -@end example - -@noindent -prints the names of bulletin boards (@code{$1}) of the file -@file{BBS-list} as a string of 10 characters, left justified. It also -prints the phone numbers (@code{$2}) afterward on the line. This -produces an aligned two-column table of names and phone numbers:@refill - -@example -@group -aardvark 555-5553 -alpo-net 555-3412 -barfly 555-7685 -bites 555-1675 -camelot 555-0542 -core 555-2912 -fooey 555-1234 -foot 555-6699 -macfoo 555-6480 -sdace 555-3430 -sabafoo 555-2127 -@end group -@end example - -Did you notice that we did not specify that the phone numbers be printed -as numbers? They had to be printed as strings because the numbers are -separated by a dash. This dash would be interpreted as a minus sign if -we had tried to print the phone numbers as numbers. This would have led -to some pretty confusing results. - -We did not specify a width for the phone numbers because they are the -last things on their lines. We don't need to put spaces after them. - -We could make our table look even nicer by adding headings to the tops -of the columns. To do this, use the @code{BEGIN} pattern -(@pxref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}) -to force the header to be printed only once, at the beginning of -the @code{awk} program:@refill - -@example -@group -awk 'BEGIN @{ print "Name Number" - print "---- ------" @} - @{ printf "%-10s %s\n", $1, $2 @}' BBS-list -@end group -@end example - -Did you notice that we mixed @code{print} and @code{printf} statements in -the above example? We could have used just @code{printf} statements to get -the same results: - -@example -@group -awk 'BEGIN @{ printf "%-10s %s\n", "Name", "Number" - printf "%-10s %s\n", "----", "------" @} - @{ printf "%-10s %s\n", $1, $2 @}' BBS-list -@end group -@end example - -@noindent -By outputting each column heading with the same format specification -used for the elements of the column, we have made sure that the headings -are aligned just like the columns. - -The fact that the same format specification is used three times can be -emphasized by storing it in a variable, like this: - -@example -awk 'BEGIN @{ format = "%-10s %s\n" - printf format, "Name", "Number" - printf format, "----", "------" @} - @{ printf format, $1, $2 @}' BBS-list -@end example - -See if you can use the @code{printf} statement to line up the headings and -table data for our @file{inventory-shipped} example covered earlier in the -section on the @code{print} statement -(@pxref{Print, ,The @code{print} Statement}).@refill - -@node Redirection, Special Files, Printf, Printing -@section Redirecting Output of @code{print} and @code{printf} - -@cindex output redirection -@cindex redirection of output -So far we have been dealing only with output that prints to the standard -output, usually your terminal. Both @code{print} and @code{printf} can -also send their output to other places. -This is called @dfn{redirection}.@refill - -A redirection appears after the @code{print} or @code{printf} statement. -Redirections in @code{awk} are written just like redirections in shell -commands, except that they are written inside the @code{awk} program. - -@menu -* File/Pipe Redirection:: Redirecting Output to Files and Pipes. -* Close Output:: How to close output files and pipes. -@end menu - -@node File/Pipe Redirection, Close Output, Redirection, Redirection -@subsection Redirecting Output to Files and Pipes - -Here are the three forms of output redirection. They are all shown for -the @code{print} statement, but they work identically for @code{printf} -also.@refill - -@table @code -@item print @var{items} > @var{output-file} -This type of redirection prints the items onto the output file -@var{output-file}. The file name @var{output-file} can be any -expression. Its value is changed to a string and then used as a -file name (@pxref{Expressions, ,Expressions as Action Statements}).@refill - -When this type of redirection is used, the @var{output-file} is erased -before the first output is written to it. Subsequent writes do not -erase @var{output-file}, but append to it. If @var{output-file} does -not exist, then it is created.@refill - -For example, here is how one @code{awk} program can write a list of -BBS names to a file @file{name-list} and a list of phone numbers to a -file @file{phone-list}. Each output file contains one name or number -per line. - -@smallexample -awk '@{ print $2 > "phone-list" - print $1 > "name-list" @}' BBS-list -@end smallexample - -@item print @var{items} >> @var{output-file} -This type of redirection prints the items onto the output file -@var{output-file}. The difference between this and the -single-@samp{>} redirection is that the old contents (if any) of -@var{output-file} are not erased. Instead, the @code{awk} output is -appended to the file. - -@cindex pipes for output -@cindex output, piping -@item print @var{items} | @var{command} -It is also possible to send output through a @dfn{pipe} instead of into a -file. This type of redirection opens a pipe to @var{command} and writes -the values of @var{items} through this pipe, to another process created -to execute @var{command}.@refill - -The redirection argument @var{command} is actually an @code{awk} -expression. Its value is converted to a string, whose contents give the -shell command to be run. - -For example, this produces two files, one unsorted list of BBS names -and one list sorted in reverse alphabetical order: - -@smallexample -awk '@{ print $1 > "names.unsorted" - print $1 | "sort -r > names.sorted" @}' BBS-list -@end smallexample - -Here the unsorted list is written with an ordinary redirection while -the sorted list is written by piping through the @code{sort} utility. - -Here is an example that uses redirection to mail a message to a mailing -list @samp{bug-system}. This might be useful when trouble is encountered -in an @code{awk} script run periodically for system maintenance. - -@smallexample -report = "mail bug-system" -print "Awk script failed:", $0 | report -print "at record number", FNR, "of", FILENAME | report -close(report) -@end smallexample - -We call the @code{close} function here because it's a good idea to close -the pipe as soon as all the intended output has been sent to it. -@xref{Close Output, ,Closing Output Files and Pipes}, for more information -on this. This example also illustrates the use of a variable to represent -a @var{file} or @var{command}: it is not necessary to always -use a string constant. Using a variable is generally a good idea, -since @code{awk} requires you to spell the string value identically -every time. -@end table - -Redirecting output using @samp{>}, @samp{>>}, or @samp{|} asks the system -to open a file or pipe only if the particular @var{file} or @var{command} -you've specified has not already been written to by your program, or if -it has been closed since it was last written to.@refill - -@node Close Output, , File/Pipe Redirection, Redirection -@subsection Closing Output Files and Pipes -@cindex closing output files and pipes -@findex close - -When a file or pipe is opened, the file name or command associated with -it is remembered by @code{awk} and subsequent writes to the same file or -command are appended to the previous writes. The file or pipe stays -open until @code{awk} exits. This is usually convenient. - -Sometimes there is a reason to close an output file or pipe earlier -than that. To do this, use the @code{close} function, as follows: - -@example -close(@var{filename}) -@end example - -@noindent -or - -@example -close(@var{command}) -@end example - -The argument @var{filename} or @var{command} can be any expression. -Its value must exactly equal the string used to open the file or pipe -to begin with---for example, if you open a pipe with this: - -@example -print $1 | "sort -r > names.sorted" -@end example - -@noindent -then you must close it with this: - -@example -close("sort -r > names.sorted") -@end example - -Here are some reasons why you might need to close an output file: - -@itemize @bullet -@item -To write a file and read it back later on in the same @code{awk} -program. Close the file when you are finished writing it; then -you can start reading it with @code{getline} -(@pxref{Getline, ,Explicit Input with @code{getline}}).@refill - -@item -To write numerous files, successively, in the same @code{awk} -program. If you don't close the files, eventually you may exceed a -system limit on the number of open files in one process. So close -each one when you are finished writing it. - -@item -To make a command finish. When you redirect output through a pipe, -the command reading the pipe normally continues to try to read input -as long as the pipe is open. Often this means the command cannot -really do its work until the pipe is closed. For example, if you -redirect output to the @code{mail} program, the message is not -actually sent until the pipe is closed. - -@item -To run the same program a second time, with the same arguments. -This is not the same thing as giving more input to the first run! - -For example, suppose you pipe output to the @code{mail} program. If you -output several lines redirected to this pipe without closing it, they make -a single message of several lines. By contrast, if you close the pipe -after each line of output, then each line makes a separate message. -@end itemize - -@iftex -@vindex ERRNO -@cindex differences: @code{gawk} and @code{awk} -@end iftex -@code{close} returns a value of zero if the close succeeded. -Otherwise, the value will be non-zero. -In this case, @code{gawk} sets the variable @code{ERRNO} to a string -describing the error that occurred. - -@node Special Files, , Redirection, Printing -@section Standard I/O Streams -@cindex standard input -@cindex standard output -@cindex standard error output -@cindex file descriptors - -Running programs conventionally have three input and output streams -already available to them for reading and writing. These are known as -the @dfn{standard input}, @dfn{standard output}, and @dfn{standard error -output}. These streams are, by default, terminal input and output, but -they are often redirected with the shell, via the @samp{<}, @samp{<<}, -@samp{>}, @samp{>>}, @samp{>&} and @samp{|} operators. Standard error -is used only for writing error messages; the reason we have two separate -streams, standard output and standard error, is so that they can be -redirected separately. - -@iftex -@cindex differences: @code{gawk} and @code{awk} -@end iftex -In other implementations of @code{awk}, the only way to write an error -message to standard error in an @code{awk} program is as follows: - -@smallexample -print "Serious error detected!\n" | "cat 1>&2" -@end smallexample - -@noindent -This works by opening a pipeline to a shell command which can access the -standard error stream which it inherits from the @code{awk} process. -This is far from elegant, and is also inefficient, since it requires a -separate process. So people writing @code{awk} programs have often -neglected to do this. Instead, they have sent the error messages to the -terminal, like this: - -@smallexample -@group -NF != 4 @{ - printf("line %d skipped: doesn't have 4 fields\n", FNR) > "/dev/tty" -@} -@end group -@end smallexample - -@noindent -This has the same effect most of the time, but not always: although the -standard error stream is usually the terminal, it can be redirected, and -when that happens, writing to the terminal is not correct. In fact, if -@code{awk} is run from a background job, it may not have a terminal at all. -Then opening @file{/dev/tty} will fail. - -@code{gawk} provides special file names for accessing the three standard -streams. When you redirect input or output in @code{gawk}, if the file name -matches one of these special names, then @code{gawk} directly uses the -stream it stands for. - -@cindex @file{/dev/stdin} -@cindex @file{/dev/stdout} -@cindex @file{/dev/stderr} -@cindex @file{/dev/fd/} -@table @file -@item /dev/stdin -The standard input (file descriptor 0). - -@item /dev/stdout -The standard output (file descriptor 1). - -@item /dev/stderr -The standard error output (file descriptor 2). - -@item /dev/fd/@var{N} -The file associated with file descriptor @var{N}. Such a file must have -been opened by the program initiating the @code{awk} execution (typically -the shell). Unless you take special pains, only descriptors 0, 1 and 2 -are available. -@end table - -The file names @file{/dev/stdin}, @file{/dev/stdout}, and @file{/dev/stderr} -are aliases for @file{/dev/fd/0}, @file{/dev/fd/1}, and @file{/dev/fd/2}, -respectively, but they are more self-explanatory. - -The proper way to write an error message in a @code{gawk} program -is to use @file{/dev/stderr}, like this: - -@smallexample -NF != 4 @{ - printf("line %d skipped: doesn't have 4 fields\n", FNR) > "/dev/stderr" -@} -@end smallexample - -@code{gawk} also provides special file names that give access to information -about the running @code{gawk} process. Each of these ``files'' provides -a single record of information. To read them more than once, you must -first close them with the @code{close} function -(@pxref{Close Input, ,Closing Input Files and Pipes}). -The filenames are: - -@cindex @file{/dev/pid} -@cindex @file{/dev/pgrpid} -@cindex @file{/dev/ppid} -@cindex @file{/dev/user} -@table @file -@item /dev/pid -Reading this file returns the process ID of the current process, -in decimal, terminated with a newline. - -@item /dev/ppid -Reading this file returns the parent process ID of the current process, -in decimal, terminated with a newline. - -@item /dev/pgrpid -Reading this file returns the process group ID of the current process, -in decimal, terminated with a newline. - -@item /dev/user -Reading this file returns a single record terminated with a newline. -The fields are separated with blanks. The fields represent the -following information: - -@table @code -@item $1 -The value of the @code{getuid} system call. - -@item $2 -The value of the @code{geteuid} system call. - -@item $3 -The value of the @code{getgid} system call. - -@item $4 -The value of the @code{getegid} system call. -@end table - -If there are any additional fields, they are the group IDs returned by -@code{getgroups} system call. -(Multiple groups may not be supported on all systems.)@refill -@end table - -These special file names may be used on the command line as data -files, as well as for I/O redirections within an @code{awk} program. -They may not be used as source files with the @samp{-f} option. - -Recognition of these special file names is disabled if @code{gawk} is in -compatibility mode (@pxref{Command Line, ,Invoking @code{awk}}). - -@quotation -@strong{Caution}: Unless your system actually has a @file{/dev/fd} directory -(or any of the other above listed special files), -the interpretation of these file names is done by @code{gawk} itself. -For example, using @samp{/dev/fd/4} for output will actually write on -file descriptor 4, and not on a new file descriptor that was @code{dup}'ed -from file descriptor 4. Most of the time this does not matter; however, it -is important to @emph{not} close any of the files related to file descriptors -0, 1, and 2. If you do close one of these files, unpredictable behavior -will result. -@end quotation - -@node One-liners, Patterns, Printing, Top -@chapter Useful ``One-liners'' - -@cindex one-liners -Useful @code{awk} programs are often short, just a line or two. Here is a -collection of useful, short programs to get you started. Some of these -programs contain constructs that haven't been covered yet. The description -of the program will give you a good idea of what is going on, but please -read the rest of the manual to become an @code{awk} expert! - -@c Per suggestions from Michal Jaegermann -@ifinfo -Since you are reading this in Info, each line of the example code is -enclosed in quotes, to represent text that you would type literally. -The examples themselves represent shell commands that use single quotes -to keep the shell from interpreting the contents of the program. -When reading the examples, focus on the text between the open and close -quotes. -@end ifinfo - -@table @code -@item awk '@{ if (NF > max) max = NF @} -@itemx @ @ @ @ @ END @{ print max @}' -This program prints the maximum number of fields on any input line. - -@item awk 'length($0) > 80' -This program prints every line longer than 80 characters. The sole -rule has a relational expression as its pattern, and has no action (so the -default action, printing the record, is used). - -@item awk 'NF > 0' -This program prints every line that has at least one field. This is an -easy way to delete blank lines from a file (or rather, to create a new -file similar to the old file but from which the blank lines have been -deleted). - -@item awk '@{ if (NF > 0) print @}' -This program also prints every line that has at least one field. Here we -allow the rule to match every line, then decide in the action whether -to print. - -@item awk@ 'BEGIN@ @{@ for (i = 1; i <= 7; i++) -@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ print int(101 * rand()) @}' -This program prints 7 random numbers from 0 to 100, inclusive. - -@item ls -l @var{files} | awk '@{ x += $4 @} ; END @{ print "total bytes: " x @}' -This program prints the total number of bytes used by @var{files}. - -@item expand@ @var{file}@ |@ awk@ '@{ if (x < length()) x = length() @} -@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ END @{ print "maximum line length is " x @}' -This program prints the maximum line length of @var{file}. The input -is piped through the @code{expand} program to change tabs into spaces, -so the widths compared are actually the right-margin columns. - -@item awk 'BEGIN @{ FS = ":" @} -@itemx @ @ @ @ @ @{ print $1 | "sort" @}' /etc/passwd -This program prints a sorted list of the login names of all users. - -@item awk '@{ nlines++ @} -@itemx @ @ @ @ @ END@ @{ print nlines @}' -This programs counts lines in a file. - -@item awk 'END @{ print NR @}' -This program also counts lines in a file, but lets @code{awk} do the work. - -@item awk '@{ print NR, $0 @}' -This program adds line numbers to all its input files, -similar to @samp{cat -n}. -@end table - -@node Patterns, Actions, One-liners, Top -@chapter Patterns -@cindex pattern, definition of - -Patterns in @code{awk} control the execution of rules: a rule is -executed when its pattern matches the current input record. This -chapter tells all about how to write patterns. - -@menu -* Kinds of Patterns:: A list of all kinds of patterns. - The following subsections describe - them in detail. -* Regexp:: Regular expressions such as @samp{/foo/}. -* Comparison Patterns:: Comparison expressions such as @code{$1 > 10}. -* Boolean Patterns:: Combining comparison expressions. -* Expression Patterns:: Any expression can be used as a pattern. -* Ranges:: Pairs of patterns specify record ranges. -* BEGIN/END:: Specifying initialization and cleanup rules. -* Empty:: The empty pattern, which matches every record. -@end menu - -@node Kinds of Patterns, Regexp, Patterns, Patterns -@section Kinds of Patterns -@cindex patterns, types of - -Here is a summary of the types of patterns supported in @code{awk}. -@c At the next rewrite, check to see that this order matches the -@c order in the text. It might not matter to a reader, but it's good -@c style. Also, it might be nice to mention all the topics of sections -@c that follow in this list; that way people can scan and know when to -@c expect a specific topic. Specifically please also make an entry -@c for Boolean operators as patterns in the right place. --mew - -@table @code -@item /@var{regular expression}/ -A regular expression as a pattern. It matches when the text of the -input record fits the regular expression. -(@xref{Regexp, ,Regular Expressions as Patterns}.)@refill - -@item @var{expression} -A single expression. It matches when its value, converted to a number, -is nonzero (if a number) or nonnull (if a string). -(@xref{Expression Patterns, ,Expressions as Patterns}.)@refill - -@item @var{pat1}, @var{pat2} -A pair of patterns separated by a comma, specifying a range of records. -(@xref{Ranges, ,Specifying Record Ranges with Patterns}.) - -@item BEGIN -@itemx END -Special patterns to supply start-up or clean-up information to -@code{awk}. (@xref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}.) - -@item @var{null} -The empty pattern matches every input record. -(@xref{Empty, ,The Empty Pattern}.)@refill -@end table - - -@node Regexp, Comparison Patterns, Kinds of Patterns, Patterns -@section Regular Expressions as Patterns -@cindex pattern, regular expressions -@cindex regexp -@cindex regular expressions as patterns - -A @dfn{regular expression}, or @dfn{regexp}, is a way of describing a -class of strings. A regular expression enclosed in slashes (@samp{/}) -is an @code{awk} pattern that matches every input record whose text -belongs to that class. - -The simplest regular expression is a sequence of letters, numbers, or -both. Such a regexp matches any string that contains that sequence. -Thus, the regexp @samp{foo} matches any string containing @samp{foo}. -Therefore, the pattern @code{/foo/} matches any input record containing -@samp{foo}. Other kinds of regexps let you specify more complicated -classes of strings. - -@menu -* Regexp Usage:: How to Use Regular Expressions -* Regexp Operators:: Regular Expression Operators -* Case-sensitivity:: How to do case-insensitive matching. -@end menu - -@node Regexp Usage, Regexp Operators, Regexp, Regexp -@subsection How to Use Regular Expressions - -A regular expression can be used as a pattern by enclosing it in -slashes. Then the regular expression is matched against the -entire text of each record. (Normally, it only needs -to match some part of the text in order to succeed.) For example, this -prints the second field of each record that contains @samp{foo} anywhere: - -@example -awk '/foo/ @{ print $2 @}' BBS-list -@end example - -@cindex regular expression matching operators -@cindex string-matching operators -@cindex operators, string-matching -@cindex operators, regexp matching -@cindex regexp search operators -Regular expressions can also be used in comparison expressions. Then -you can specify the string to match against; it need not be the entire -current input record. These comparison expressions can be used as -patterns or in @code{if}, @code{while}, @code{for}, and @code{do} statements. - -@table @code -@item @var{exp} ~ /@var{regexp}/ -This is true if the expression @var{exp} (taken as a character string) -is matched by @var{regexp}. The following example matches, or selects, -all input records with the upper-case letter @samp{J} somewhere in the -first field:@refill - -@example -awk '$1 ~ /J/' inventory-shipped -@end example - -So does this: - -@example -awk '@{ if ($1 ~ /J/) print @}' inventory-shipped -@end example - -@item @var{exp} !~ /@var{regexp}/ -This is true if the expression @var{exp} (taken as a character string) -is @emph{not} matched by @var{regexp}. The following example matches, -or selects, all input records whose first field @emph{does not} contain -the upper-case letter @samp{J}:@refill - -@example -awk '$1 !~ /J/' inventory-shipped -@end example -@end table - -@cindex computed regular expressions -@cindex regular expressions, computed -@cindex dynamic regular expressions -The right hand side of a @samp{~} or @samp{!~} operator need not be a -constant regexp (i.e., a string of characters between slashes). It may -be any expression. The expression is evaluated, and converted if -necessary to a string; the contents of the string are used as the -regexp. A regexp that is computed in this way is called a @dfn{dynamic -regexp}. For example: - -@example -identifier_regexp = "[A-Za-z_][A-Za-z_0-9]+" -$0 ~ identifier_regexp -@end example - -@noindent -sets @code{identifier_regexp} to a regexp that describes @code{awk} -variable names, and tests if the input record matches this regexp. - -@node Regexp Operators, Case-sensitivity, Regexp Usage, Regexp -@subsection Regular Expression Operators -@cindex metacharacters -@cindex regular expression metacharacters - -You can combine regular expressions with the following characters, -called @dfn{regular expression operators}, or @dfn{metacharacters}, to -increase the power and versatility of regular expressions. - -Here is a table of metacharacters. All characters not listed in the -table stand for themselves. - -@table @code -@item ^ -This matches the beginning of the string or the beginning of a line -within the string. For example: - -@example -^@@chapter -@end example - -@noindent -matches the @samp{@@chapter} at the beginning of a string, and can be used -to identify chapter beginnings in Texinfo source files. - -@item $ -This is similar to @samp{^}, but it matches only at the end of a string -or the end of a line within the string. For example: - -@example -p$ -@end example - -@noindent -matches a record that ends with a @samp{p}. - -@item . -This matches any single character except a newline. For example: - -@example -.P -@end example - -@noindent -matches any single character followed by a @samp{P} in a string. Using -concatenation we can make regular expressions like @samp{U.A}, which -matches any three-character sequence that begins with @samp{U} and ends -with @samp{A}. - -@item [@dots{}] -This is called a @dfn{character set}. It matches any one of the -characters that are enclosed in the square brackets. For example: - -@example -[MVX] -@end example - -@noindent -matches any one of the characters @samp{M}, @samp{V}, or @samp{X} in a -string.@refill - -Ranges of characters are indicated by using a hyphen between the beginning -and ending characters, and enclosing the whole thing in brackets. For -example:@refill - -@example -[0-9] -@end example - -@noindent -matches any digit. - -To include the character @samp{\}, @samp{]}, @samp{-} or @samp{^} in a -character set, put a @samp{\} in front of it. For example: - -@example -[d\]] -@end example - -@noindent -matches either @samp{d}, or @samp{]}.@refill - -This treatment of @samp{\} is compatible with other @code{awk} -implementations, and is also mandated by the @sc{posix} Command Language -and Utilities standard. The regular expressions in @code{awk} are a superset -of the @sc{posix} specification for Extended Regular Expressions (EREs). -@sc{posix} EREs are based on the regular expressions accepted by the -traditional @code{egrep} utility. - -In @code{egrep} syntax, backslash is not syntactically special within -square brackets. This means that special tricks have to be used to -represent the characters @samp{]}, @samp{-} and @samp{^} as members of a -character set. - -In @code{egrep} syntax, to match @samp{-}, write it as @samp{---}, -which is a range containing only @w{@samp{-}.} You may also give @samp{-} -as the first or last character in the set. To match @samp{^}, put it -anywhere except as the first character of a set. To match a @samp{]}, -make it the first character in the set. For example:@refill - -@example -[]d^] -@end example - -@noindent -matches either @samp{]}, @samp{d} or @samp{^}.@refill - -@item [^ @dots{}] -This is a @dfn{complemented character set}. The first character after -the @samp{[} @emph{must} be a @samp{^}. It matches any characters -@emph{except} those in the square brackets (or newline). For example: - -@example -[^0-9] -@end example - -@noindent -matches any character that is not a digit. - -@item | -This is the @dfn{alternation operator} and it is used to specify -alternatives. For example: - -@example -^P|[0-9] -@end example - -@noindent -matches any string that matches either @samp{^P} or @samp{[0-9]}. This -means it matches any string that contains a digit or starts with @samp{P}. - -The alternation applies to the largest possible regexps on either side. -@item (@dots{}) -Parentheses are used for grouping in regular expressions as in -arithmetic. They can be used to concatenate regular expressions -containing the alternation operator, @samp{|}. - -@item * -This symbol means that the preceding regular expression is to be -repeated as many times as possible to find a match. For example: - -@example -ph* -@end example - -@noindent -applies the @samp{*} symbol to the preceding @samp{h} and looks for matches -to one @samp{p} followed by any number of @samp{h}s. This will also match -just @samp{p} if no @samp{h}s are present. - -The @samp{*} repeats the @emph{smallest} possible preceding expression. -(Use parentheses if you wish to repeat a larger expression.) It finds -as many repetitions as possible. For example: - -@example -awk '/\(c[ad][ad]*r x\)/ @{ print @}' sample -@end example - -@noindent -prints every record in the input containing a string of the form -@samp{(car x)}, @samp{(cdr x)}, @samp{(cadr x)}, and so on.@refill - -@item + -This symbol is similar to @samp{*}, but the preceding expression must be -matched at least once. This means that: - -@example -wh+y -@end example - -@noindent -would match @samp{why} and @samp{whhy} but not @samp{wy}, whereas -@samp{wh*y} would match all three of these strings. This is a simpler -way of writing the last @samp{*} example: - -@example -awk '/\(c[ad]+r x\)/ @{ print @}' sample -@end example - -@item ? -This symbol is similar to @samp{*}, but the preceding expression can be -matched once or not at all. For example: - -@example -fe?d -@end example - -@noindent -will match @samp{fed} and @samp{fd}, but nothing else.@refill - -@item \ -This is used to suppress the special meaning of a character when -matching. For example: - -@example -\$ -@end example - -@noindent -matches the character @samp{$}. - -The escape sequences used for string constants -(@pxref{Constants, ,Constant Expressions}) are -valid in regular expressions as well; they are also introduced by a -@samp{\}.@refill -@end table - -In regular expressions, the @samp{*}, @samp{+}, and @samp{?} operators have -the highest precedence, followed by concatenation, and finally by @samp{|}. -As in arithmetic, parentheses can change how operators are grouped.@refill - -@node Case-sensitivity, , Regexp Operators, Regexp -@subsection Case-sensitivity in Matching - -Case is normally significant in regular expressions, both when matching -ordinary characters (i.e., not metacharacters), and inside character -sets. Thus a @samp{w} in a regular expression matches only a lower case -@samp{w} and not an upper case @samp{W}. - -The simplest way to do a case-independent match is to use a character -set: @samp{[Ww]}. However, this can be cumbersome if you need to use it -often; and it can make the regular expressions harder for humans to -read. There are two other alternatives that you might prefer. - -One way to do a case-insensitive match at a particular point in the -program is to convert the data to a single case, using the -@code{tolower} or @code{toupper} built-in string functions (which we -haven't discussed yet; -@pxref{String Functions, ,Built-in Functions for String Manipulation}). -For example:@refill - -@example -tolower($1) ~ /foo/ @{ @dots{} @} -@end example - -@noindent -converts the first field to lower case before matching against it. - -Another method is to set the variable @code{IGNORECASE} to a nonzero -value (@pxref{Built-in Variables}). When @code{IGNORECASE} is not zero, -@emph{all} regexp operations ignore case. Changing the value of -@code{IGNORECASE} dynamically controls the case sensitivity of your -program as it runs. Case is significant by default because -@code{IGNORECASE} (like most variables) is initialized to zero. - -@example -x = "aB" -if (x ~ /ab/) @dots{} # this test will fail - -IGNORECASE = 1 -if (x ~ /ab/) @dots{} # now it will succeed -@end example - -In general, you cannot use @code{IGNORECASE} to make certain rules -case-insensitive and other rules case-sensitive, because there is no way -to set @code{IGNORECASE} just for the pattern of a particular rule. To -do this, you must use character sets or @code{tolower}. However, one -thing you can do only with @code{IGNORECASE} is turn case-sensitivity on -or off dynamically for all the rules at once.@refill - -@code{IGNORECASE} can be set on the command line, or in a @code{BEGIN} -rule. Setting @code{IGNORECASE} from the command line is a way to make -a program case-insensitive without having to edit it. - -The value of @code{IGNORECASE} has no effect if @code{gawk} is in -compatibility mode (@pxref{Command Line, ,Invoking @code{awk}}). -Case is always significant in compatibility mode.@refill - -@node Comparison Patterns, Boolean Patterns, Regexp, Patterns -@section Comparison Expressions as Patterns -@cindex comparison expressions as patterns -@cindex pattern, comparison expressions -@cindex relational operators -@cindex operators, relational - -@dfn{Comparison patterns} test relationships such as equality between -two strings or numbers. They are a special case of expression patterns -(@pxref{Expression Patterns, ,Expressions as Patterns}). They are written -with @dfn{relational operators}, which are a superset of those in C. -Here is a table of them:@refill - -@table @code -@item @var{x} < @var{y} -True if @var{x} is less than @var{y}. - -@item @var{x} <= @var{y} -True if @var{x} is less than or equal to @var{y}. - -@item @var{x} > @var{y} -True if @var{x} is greater than @var{y}. - -@item @var{x} >= @var{y} -True if @var{x} is greater than or equal to @var{y}. - -@item @var{x} == @var{y} -True if @var{x} is equal to @var{y}. - -@item @var{x} != @var{y} -True if @var{x} is not equal to @var{y}. - -@item @var{x} ~ @var{y} -True if @var{x} matches the regular expression described by @var{y}. - -@item @var{x} !~ @var{y} -True if @var{x} does not match the regular expression described by @var{y}. -@end table - -The operands of a relational operator are compared as numbers if they -are both numbers. Otherwise they are converted to, and compared as, -strings (@pxref{Conversion, ,Conversion of Strings and Numbers}, -for the detailed rules). Strings are compared by comparing the first -character of each, then the second character of each, -and so on, until there is a difference. If the two strings are equal until -the shorter one runs out, the shorter one is considered to be less than the -longer one. Thus, @code{"10"} is less than @code{"9"}, and @code{"abc"} -is less than @code{"abcd"}.@refill - -The left operand of the @samp{~} and @samp{!~} operators is a string. -The right operand is either a constant regular expression enclosed in -slashes (@code{/@var{regexp}/}), or any expression, whose string value -is used as a dynamic regular expression -(@pxref{Regexp Usage, ,How to Use Regular Expressions}).@refill - -The following example prints the second field of each input record -whose first field is precisely @samp{foo}. - -@example -awk '$1 == "foo" @{ print $2 @}' BBS-list -@end example - -@noindent -Contrast this with the following regular expression match, which would -accept any record with a first field that contains @samp{foo}: - -@example -awk '$1 ~ "foo" @{ print $2 @}' BBS-list -@end example - -@noindent -or, equivalently, this one: - -@example -awk '$1 ~ /foo/ @{ print $2 @}' BBS-list -@end example - -@node Boolean Patterns, Expression Patterns, Comparison Patterns, Patterns -@section Boolean Operators and Patterns -@cindex patterns, boolean -@cindex boolean patterns - -A @dfn{boolean pattern} is an expression which combines other patterns -using the @dfn{boolean operators} ``or'' (@samp{||}), ``and'' -(@samp{&&}), and ``not'' (@samp{!}). Whether the boolean pattern -matches an input record depends on whether its subpatterns match. - -For example, the following command prints all records in the input file -@file{BBS-list} that contain both @samp{2400} and @samp{foo}.@refill - -@example -awk '/2400/ && /foo/' BBS-list -@end example - -The following command prints all records in the input file -@file{BBS-list} that contain @emph{either} @samp{2400} or @samp{foo}, or -both.@refill - -@example -awk '/2400/ || /foo/' BBS-list -@end example - -The following command prints all records in the input file -@file{BBS-list} that do @emph{not} contain the string @samp{foo}. - -@example -awk '! /foo/' BBS-list -@end example - -Note that boolean patterns are a special case of expression patterns -(@pxref{Expression Patterns, ,Expressions as Patterns}); they are -expressions that use the boolean operators. -@xref{Boolean Ops, ,Boolean Expressions}, for complete information -on the boolean operators.@refill - -The subpatterns of a boolean pattern can be constant regular -expressions, comparisons, or any other @code{awk} expressions. Range -patterns are not expressions, so they cannot appear inside boolean -patterns. Likewise, the special patterns @code{BEGIN} and @code{END}, -which never match any input record, are not expressions and cannot -appear inside boolean patterns. - -@node Expression Patterns, Ranges, Boolean Patterns, Patterns -@section Expressions as Patterns - -Any @code{awk} expression is also valid as an @code{awk} pattern. -Then the pattern ``matches'' if the expression's value is nonzero (if a -number) or nonnull (if a string). - -The expression is reevaluated each time the rule is tested against a new -input record. If the expression uses fields such as @code{$1}, the -value depends directly on the new input record's text; otherwise, it -depends only on what has happened so far in the execution of the -@code{awk} program, but that may still be useful. - -Comparison patterns are actually a special case of this. For -example, the expression @code{$5 == "foo"} has the value 1 when the -value of @code{$5} equals @code{"foo"}, and 0 otherwise; therefore, this -expression as a pattern matches when the two values are equal. - -Boolean patterns are also special cases of expression patterns. - -A constant regexp as a pattern is also a special case of an expression -pattern. @code{/foo/} as an expression has the value 1 if @samp{foo} -appears in the current input record; thus, as a pattern, @code{/foo/} -matches any record containing @samp{foo}. - -Other implementations of @code{awk} that are not yet @sc{posix} compliant -are less general than @code{gawk}: they allow comparison expressions, and -boolean combinations thereof (optionally with parentheses), but not -necessarily other kinds of expressions. - -@node Ranges, BEGIN/END, Expression Patterns, Patterns -@section Specifying Record Ranges with Patterns - -@cindex range pattern -@cindex patterns, range -A @dfn{range pattern} is made of two patterns separated by a comma, of -the form @code{@var{begpat}, @var{endpat}}. It matches ranges of -consecutive input records. The first pattern @var{begpat} controls -where the range begins, and the second one @var{endpat} controls where -it ends. For example,@refill - -@example -awk '$1 == "on", $1 == "off"' -@end example - -@noindent -prints every record between @samp{on}/@samp{off} pairs, inclusive. - -A range pattern starts out by matching @var{begpat} -against every input record; when a record matches @var{begpat}, the -range pattern becomes @dfn{turned on}. The range pattern matches this -record. As long as it stays turned on, it automatically matches every -input record read. It also matches @var{endpat} against -every input record; when that succeeds, the range pattern is turned -off again for the following record. Now it goes back to checking -@var{begpat} against each record. - -The record that turns on the range pattern and the one that turns it -off both match the range pattern. If you don't want to operate on -these records, you can write @code{if} statements in the rule's action -to distinguish them. - -It is possible for a pattern to be turned both on and off by the same -record, if both conditions are satisfied by that record. Then the action is -executed for just that record. - -@node BEGIN/END, Empty, Ranges, Patterns -@section @code{BEGIN} and @code{END} Special Patterns - -@cindex @code{BEGIN} special pattern -@cindex patterns, @code{BEGIN} -@cindex @code{END} special pattern -@cindex patterns, @code{END} -@code{BEGIN} and @code{END} are special patterns. They are not used to -match input records. Rather, they are used for supplying start-up or -clean-up information to your @code{awk} script. A @code{BEGIN} rule is -executed, once, before the first input record has been read. An @code{END} -rule is executed, once, after all the input has been read. For -example:@refill - -@example -awk 'BEGIN @{ print "Analysis of `foo'" @} - /foo/ @{ ++foobar @} - END @{ print "`foo' appears " foobar " times." @}' BBS-list -@end example - -This program finds the number of records in the input file @file{BBS-list} -that contain the string @samp{foo}. The @code{BEGIN} rule prints a title -for the report. There is no need to use the @code{BEGIN} rule to -initialize the counter @code{foobar} to zero, as @code{awk} does this -for us automatically (@pxref{Variables}). - -The second rule increments the variable @code{foobar} every time a -record containing the pattern @samp{foo} is read. The @code{END} rule -prints the value of @code{foobar} at the end of the run.@refill - -The special patterns @code{BEGIN} and @code{END} cannot be used in ranges -or with boolean operators (indeed, they cannot be used with any operators). - -An @code{awk} program may have multiple @code{BEGIN} and/or @code{END} -rules. They are executed in the order they appear, all the @code{BEGIN} -rules at start-up and all the @code{END} rules at termination. - -Multiple @code{BEGIN} and @code{END} sections are useful for writing -library functions, since each library can have its own @code{BEGIN} or -@code{END} rule to do its own initialization and/or cleanup. Note that -the order in which library functions are named on the command line -controls the order in which their @code{BEGIN} and @code{END} rules are -executed. Therefore you have to be careful to write such rules in -library files so that the order in which they are executed doesn't matter. -@xref{Command Line, ,Invoking @code{awk}}, for more information on -using library functions. - -If an @code{awk} program only has a @code{BEGIN} rule, and no other -rules, then the program exits after the @code{BEGIN} rule has been run. -(Older versions of @code{awk} used to keep reading and ignoring input -until end of file was seen.) However, if an @code{END} rule exists as -well, then the input will be read, even if there are no other rules in -the program. This is necessary in case the @code{END} rule checks the -@code{NR} variable. - -@code{BEGIN} and @code{END} rules must have actions; there is no default -action for these rules since there is no current record when they run. - -@node Empty, , BEGIN/END, Patterns -@comment node-name, next, previous, up -@section The Empty Pattern - -@cindex empty pattern -@cindex pattern, empty -An empty pattern is considered to match @emph{every} input record. For -example, the program:@refill - -@example -awk '@{ print $1 @}' BBS-list -@end example - -@noindent -prints the first field of every record. - -@node Actions, Expressions, Patterns, Top -@chapter Overview of Actions -@cindex action, definition of -@cindex curly braces -@cindex action, curly braces -@cindex action, separating statements - -An @code{awk} program or script consists of a series of -rules and function definitions, interspersed. (Functions are -described later. @xref{User-defined, ,User-defined Functions}.) - -A rule contains a pattern and an action, either of which may be -omitted. The purpose of the @dfn{action} is to tell @code{awk} what to do -once a match for the pattern is found. Thus, the entire program -looks somewhat like this: - -@example -@r{[}@var{pattern}@r{]} @r{[}@{ @var{action} @}@r{]} -@r{[}@var{pattern}@r{]} @r{[}@{ @var{action} @}@r{]} -@dots{} -function @var{name} (@var{args}) @{ @dots{} @} -@dots{} -@end example - -An action consists of one or more @code{awk} @dfn{statements}, enclosed -in curly braces (@samp{@{} and @samp{@}}). Each statement specifies one -thing to be done. The statements are separated by newlines or -semicolons. - -The curly braces around an action must be used even if the action -contains only one statement, or even if it contains no statements at -all. However, if you omit the action entirely, omit the curly braces as -well. (An omitted action is equivalent to @samp{@{ print $0 @}}.) - -Here are the kinds of statements supported in @code{awk}: - -@itemize @bullet -@item -Expressions, which can call functions or assign values to variables -(@pxref{Expressions, ,Expressions as Action Statements}). Executing -this kind of statement simply computes the value of the expression and -then ignores it. This is useful when the expression has side effects -(@pxref{Assignment Ops, ,Assignment Expressions}).@refill - -@item -Control statements, which specify the control flow of @code{awk} -programs. The @code{awk} language gives you C-like constructs -(@code{if}, @code{for}, @code{while}, and so on) as well as a few -special ones (@pxref{Statements, ,Control Statements in Actions}).@refill - -@item -Compound statements, which consist of one or more statements enclosed in -curly braces. A compound statement is used in order to put several -statements together in the body of an @code{if}, @code{while}, @code{do} -or @code{for} statement. - -@item -Input control, using the @code{getline} command -(@pxref{Getline, ,Explicit Input with @code{getline}}), and the @code{next} -statement (@pxref{Next Statement, ,The @code{next} Statement}). - -@item -Output statements, @code{print} and @code{printf}. -@xref{Printing, ,Printing Output}.@refill - -@item -Deletion statements, for deleting array elements. -@xref{Delete, ,The @code{delete} Statement}.@refill -@end itemize - -@iftex -The next two chapters cover in detail expressions and control -statements, respectively. We go on to treat arrays and built-in -functions, both of which are used in expressions. Then we proceed -to discuss how to define your own functions. -@end iftex - -@node Expressions, Statements, Actions, Top -@chapter Expressions as Action Statements -@cindex expression - -Expressions are the basic building block of @code{awk} actions. An -expression evaluates to a value, which you can print, test, store in a -variable or pass to a function. But beyond that, an expression can assign a new value to a variable -or a field, with an assignment operator. - -An expression can serve as a statement on its own. Most other kinds of -statements contain one or more expressions which specify data to be -operated on. As in other languages, expressions in @code{awk} include -variables, array references, constants, and function calls, as well as -combinations of these with various operators. - -@menu -* Constants:: String, numeric, and regexp constants. -* Variables:: Variables give names to values for later use. -* Arithmetic Ops:: Arithmetic operations (@samp{+}, @samp{-}, etc.) -* Concatenation:: Concatenating strings. -* Comparison Ops:: Comparison of numbers and strings - with @samp{<}, etc. -* Boolean Ops:: Combining comparison expressions - using boolean operators - @samp{||} (``or''), @samp{&&} (``and'') and @samp{!} (``not''). - -* Assignment Ops:: Changing the value of a variable or a field. -* Increment Ops:: Incrementing the numeric value of a variable. - -* Conversion:: The conversion of strings to numbers - and vice versa. -* Values:: The whole truth about numbers and strings. -* Conditional Exp:: Conditional expressions select - between two subexpressions under control - of a third subexpression. -* Function Calls:: A function call is an expression. -* Precedence:: How various operators nest. -@end menu - -@node Constants, Variables, Expressions, Expressions -@section Constant Expressions -@cindex constants, types of -@cindex string constants - -The simplest type of expression is the @dfn{constant}, which always has -the same value. There are three types of constants: numeric constants, -string constants, and regular expression constants. - -@cindex numeric constant -@cindex numeric value -A @dfn{numeric constant} stands for a number. This number can be an -integer, a decimal fraction, or a number in scientific (exponential) -notation. Note that all numeric values are represented within -@code{awk} in double-precision floating point. Here are some examples -of numeric constants, which all have the same value: - -@example -105 -1.05e+2 -1050e-1 -@end example - -A string constant consists of a sequence of characters enclosed in -double-quote marks. For example: - -@example -"parrot" -@end example - -@noindent -@iftex -@cindex differences between @code{gawk} and @code{awk} -@end iftex -represents the string whose contents are @samp{parrot}. Strings in -@code{gawk} can be of any length and they can contain all the possible -8-bit ASCII characters including ASCII NUL. Other @code{awk} -implementations may have difficulty with some character codes.@refill - -@cindex escape sequence notation -Some characters cannot be included literally in a string constant. You -represent them instead with @dfn{escape sequences}, which are character -sequences beginning with a backslash (@samp{\}). - -One use of an escape sequence is to include a double-quote character in -a string constant. Since a plain double-quote would end the string, you -must use @samp{\"} to represent a single double-quote character as a -part of the string. -The -backslash character itself is another character that cannot be -included normally; you write @samp{\\} to put one backslash in the -string. Thus, the string whose contents are the two characters -@samp{"\} must be written @code{"\"\\"}. - -Another use of backslash is to represent unprintable characters -such as newline. While there is nothing to stop you from writing most -of these characters directly in a string constant, they may look ugly. - -Here is a table of all the escape sequences used in @code{awk}: - -@table @code -@item \\ -Represents a literal backslash, @samp{\}. - -@item \a -Represents the ``alert'' character, control-g, ASCII code 7. - -@item \b -Represents a backspace, control-h, ASCII code 8. - -@item \f -Represents a formfeed, control-l, ASCII code 12. - -@item \n -Represents a newline, control-j, ASCII code 10. - -@item \r -Represents a carriage return, control-m, ASCII code 13. - -@item \t -Represents a horizontal tab, control-i, ASCII code 9. - -@item \v -Represents a vertical tab, control-k, ASCII code 11. - -@item \@var{nnn} -Represents the octal value @var{nnn}, where @var{nnn} are one to three -digits between 0 and 7. For example, the code for the ASCII ESC -(escape) character is @samp{\033}.@refill - -@item \x@var{hh}@dots{} -Represents the hexadecimal value @var{hh}, where @var{hh} are hexadecimal -digits (@samp{0} through @samp{9} and either @samp{A} through @samp{F} or -@samp{a} through @samp{f}). Like the same construct in @sc{ansi} C, the escape -sequence continues until the first non-hexadecimal digit is seen. However, -using more than two hexadecimal digits produces undefined results. (The -@samp{\x} escape sequence is not allowed in @sc{posix} @code{awk}.)@refill -@end table - -A @dfn{constant regexp} is a regular expression description enclosed in -slashes, such as @code{/^beginning and end$/}. Most regexps used in -@code{awk} programs are constant, but the @samp{~} and @samp{!~} -operators can also match computed or ``dynamic'' regexps -(@pxref{Regexp Usage, ,How to Use Regular Expressions}).@refill - -Constant regexps may be used like simple expressions. When a -constant regexp is not on the right hand side of the @samp{~} or -@samp{!~} operators, it has the same meaning as if it appeared -in a pattern, i.e. @samp{($0 ~ /foo/)} -(@pxref{Expression Patterns, ,Expressions as Patterns}). -This means that the two code segments,@refill - -@example -if ($0 ~ /barfly/ || $0 ~ /camelot/) - print "found" -@end example - -@noindent -and - -@example -if (/barfly/ || /camelot/) - print "found" -@end example - -@noindent -are exactly equivalent. One rather bizarre consequence of this rule is -that the following boolean expression is legal, but does not do what the user -intended:@refill - -@example -if (/foo/ ~ $1) print "found foo" -@end example - -This code is ``obviously'' testing @code{$1} for a match against the regexp -@code{/foo/}. But in fact, the expression @code{(/foo/ ~ $1)} actually means -@code{(($0 ~ /foo/) ~ $1)}. In other words, first match the input record -against the regexp @code{/foo/}. The result will be either a 0 or a 1, -depending upon the success or failure of the match. Then match that result -against the first field in the record.@refill - -Since it is unlikely that you would ever really wish to make this kind of -test, @code{gawk} will issue a warning when it sees this construct in -a program.@refill - -Another consequence of this rule is that the assignment statement - -@example -matches = /foo/ -@end example - -@noindent -will assign either 0 or 1 to the variable @code{matches}, depending -upon the contents of the current input record. - -Constant regular expressions are also used as the first argument for -the @code{sub} and @code{gsub} functions -(@pxref{String Functions, ,Built-in Functions for String Manipulation}).@refill - -This feature of the language was never well documented until the -@sc{posix} specification. - -You may be wondering, when is - -@example -$1 ~ /foo/ @{ @dots{} @} -@end example - -@noindent -preferable to - -@example -$1 ~ "foo" @{ @dots{} @} -@end example - -Since the right-hand sides of both @samp{~} operators are constants, -it is more efficient to use the @samp{/foo/} form: @code{awk} can note -that you have supplied a regexp and store it internally in a form that -makes pattern matching more efficient. In the second form, @code{awk} -must first convert the string into this internal form, and then perform -the pattern matching. The first form is also better style; it shows -clearly that you intend a regexp match. - -@node Variables, Arithmetic Ops, Constants, Expressions -@section Variables -@cindex variables, user-defined -@cindex user-defined variables -@c there should be more than one subsection, ideally. Not a big deal. -@c But usually there are supposed to be at least two. One way to get -@c around this is to write the info in the subsection as the info in the -@c section itself and not have any subsections.. --mew - -Variables let you give names to values and refer to them later. You have -already seen variables in many of the examples. The name of a variable -must be a sequence of letters, digits and underscores, but it may not begin -with a digit. Case is significant in variable names; @code{a} and @code{A} -are distinct variables. - -A variable name is a valid expression by itself; it represents the -variable's current value. Variables are given new values with -@dfn{assignment operators} and @dfn{increment operators}. -@xref{Assignment Ops, ,Assignment Expressions}. - -A few variables have special built-in meanings, such as @code{FS}, the -field separator, and @code{NF}, the number of fields in the current -input record. @xref{Built-in Variables}, for a list of them. These -built-in variables can be used and assigned just like all other -variables, but their values are also used or changed automatically by -@code{awk}. Each built-in variable's name is made entirely of upper case -letters. - -Variables in @code{awk} can be assigned either numeric or string -values. By default, variables are initialized to the null string, which -is effectively zero if converted to a number. There is no need to -``initialize'' each variable explicitly in @code{awk}, the way you would in C or most other traditional languages. - -@menu -* Assignment Options:: Setting variables on the command line - and a summary of command line syntax. - This is an advanced method of input. -@end menu - -@node Assignment Options, , Variables, Variables -@subsection Assigning Variables on the Command Line - -You can set any @code{awk} variable by including a @dfn{variable assignment} -among the arguments on the command line when you invoke @code{awk} -(@pxref{Command Line, ,Invoking @code{awk}}). Such an assignment has -this form:@refill - -@example -@var{variable}=@var{text} -@end example - -@noindent -With it, you can set a variable either at the beginning of the -@code{awk} run or in between input files. - -If you precede the assignment with the @samp{-v} option, like this: - -@example --v @var{variable}=@var{text} -@end example - -@noindent -then the variable is set at the very beginning, before even the -@code{BEGIN} rules are run. The @samp{-v} option and its assignment -must precede all the file name arguments, as well as the program text. - -Otherwise, the variable assignment is performed at a time determined by -its position among the input file arguments: after the processing of the -preceding input file argument. For example: - -@example -awk '@{ print $n @}' n=4 inventory-shipped n=2 BBS-list -@end example - -@noindent -prints the value of field number @code{n} for all input records. Before -the first file is read, the command line sets the variable @code{n} -equal to 4. This causes the fourth field to be printed in lines from -the file @file{inventory-shipped}. After the first file has finished, -but before the second file is started, @code{n} is set to 2, so that the -second field is printed in lines from @file{BBS-list}. - -Command line arguments are made available for explicit examination by -the @code{awk} program in an array named @code{ARGV} -(@pxref{Built-in Variables}).@refill - -@code{awk} processes the values of command line assignments for escape -sequences (@pxref{Constants, ,Constant Expressions}). - -@node Arithmetic Ops, Concatenation, Variables, Expressions -@section Arithmetic Operators -@cindex arithmetic operators -@cindex operators, arithmetic -@cindex addition -@cindex subtraction -@cindex multiplication -@cindex division -@cindex remainder -@cindex quotient -@cindex exponentiation - -The @code{awk} language uses the common arithmetic operators when -evaluating expressions. All of these arithmetic operators follow normal -precedence rules, and work as you would expect them to. This example -divides field three by field four, adds field two, stores the result -into field one, and prints the resulting altered input record: - -@example -awk '@{ $1 = $2 + $3 / $4; print @}' inventory-shipped -@end example - -The arithmetic operators in @code{awk} are: - -@table @code -@item @var{x} + @var{y} -Addition. - -@item @var{x} - @var{y} -Subtraction. - -@item - @var{x} -Negation. - -@item + @var{x} -Unary plus. No real effect on the expression. - -@item @var{x} * @var{y} -Multiplication. - -@item @var{x} / @var{y} -Division. Since all numbers in @code{awk} are double-precision -floating point, the result is not rounded to an integer: @code{3 / 4} -has the value 0.75. - -@item @var{x} % @var{y} -@iftex -@cindex differences between @code{gawk} and @code{awk} -@end iftex -Remainder. The quotient is rounded toward zero to an integer, -multiplied by @var{y} and this result is subtracted from @var{x}. -This operation is sometimes known as ``trunc-mod.'' The following -relation always holds: - -@example -b * int(a / b) + (a % b) == a -@end example - -One possibly undesirable effect of this definition of remainder is that -@code{@var{x} % @var{y}} is negative if @var{x} is negative. Thus, - -@example --17 % 8 = -1 -@end example - -In other @code{awk} implementations, the signedness of the remainder -may be machine dependent. - -@item @var{x} ^ @var{y} -@itemx @var{x} ** @var{y} -Exponentiation: @var{x} raised to the @var{y} power. @code{2 ^ 3} has -the value 8. The character sequence @samp{**} is equivalent to -@samp{^}. (The @sc{posix} standard only specifies the use of @samp{^} -for exponentiation.) -@end table - -@node Concatenation, Comparison Ops, Arithmetic Ops, Expressions -@section String Concatenation - -@cindex string operators -@cindex operators, string -@cindex concatenation -There is only one string operation: concatenation. It does not have a -specific operator to represent it. Instead, concatenation is performed by -writing expressions next to one another, with no operator. For example: - -@example -awk '@{ print "Field number one: " $1 @}' BBS-list -@end example - -@noindent -produces, for the first record in @file{BBS-list}: - -@example -Field number one: aardvark -@end example - -Without the space in the string constant after the @samp{:}, the line -would run together. For example: - -@example -awk '@{ print "Field number one:" $1 @}' BBS-list -@end example - -@noindent -produces, for the first record in @file{BBS-list}: - -@example -Field number one:aardvark -@end example - -Since string concatenation does not have an explicit operator, it is -often necessary to insure that it happens where you want it to by -enclosing the items to be concatenated in parentheses. For example, the -following code fragment does not concatenate @code{file} and @code{name} -as you might expect: - -@example -file = "file" -name = "name" -print "something meaningful" > file name -@end example - -@noindent -It is necessary to use the following: - -@example -print "something meaningful" > (file name) -@end example - -We recommend you use parentheses around concatenation in all but the -most common contexts (such as in the right-hand operand of @samp{=}). - -@ignore -@code{gawk} actually now allows a concatenation on the right hand -side of a @code{>} redirection, but other @code{awk}s don't. So for -now we won't mention that fact. -@end ignore - -@node Comparison Ops, Boolean Ops, Concatenation, Expressions -@section Comparison Expressions -@cindex comparison expressions -@cindex expressions, comparison -@cindex relational operators -@cindex operators, relational -@cindex regexp operators - -@dfn{Comparison expressions} compare strings or numbers for -relationships such as equality. They are written using @dfn{relational -operators}, which are a superset of those in C. Here is a table of -them: - -@table @code -@item @var{x} < @var{y} -True if @var{x} is less than @var{y}. - -@item @var{x} <= @var{y} -True if @var{x} is less than or equal to @var{y}. - -@item @var{x} > @var{y} -True if @var{x} is greater than @var{y}. - -@item @var{x} >= @var{y} -True if @var{x} is greater than or equal to @var{y}. - -@item @var{x} == @var{y} -True if @var{x} is equal to @var{y}. - -@item @var{x} != @var{y} -True if @var{x} is not equal to @var{y}. - -@item @var{x} ~ @var{y} -True if the string @var{x} matches the regexp denoted by @var{y}. - -@item @var{x} !~ @var{y} -True if the string @var{x} does not match the regexp denoted by @var{y}. - -@item @var{subscript} in @var{array} -True if array @var{array} has an element with the subscript @var{subscript}. -@end table - -Comparison expressions have the value 1 if true and 0 if false. - -The rules @code{gawk} uses for performing comparisons are based on those -in draft 11.2 of the @sc{posix} standard. The @sc{posix} standard introduced -the concept of a @dfn{numeric string}, which is simply a string that looks -like a number, for example, @code{@w{" +2"}}. - -@vindex CONVFMT -When performing a relational operation, @code{gawk} considers the type of an -operand to be the type it received on its last @emph{assignment}, rather -than the type of its last @emph{use} -(@pxref{Values, ,Numeric and String Values}). -This type is @emph{unknown} when the operand is from an ``external'' source: -field variables, command line arguments, array elements resulting from a -@code{split} operation, and the value of an @code{ENVIRON} element. -In this case only, if the operand is a numeric string, then it is -considered to be of both string type and numeric type. If at least one -operand of a comparison is of string type only, then a string -comparison is performed. Any numeric operand will be converted to a -string using the value of @code{CONVFMT} -(@pxref{Conversion, ,Conversion of Strings and Numbers}). -If one operand of a comparison is numeric, and the other operand is -either numeric or both numeric and string, then @code{gawk} does a -numeric comparison. If both operands have both types, then the -comparison is numeric. Strings are compared -by comparing the first character of each, then the second character of each, -and so on. Thus @code{"10"} is less than @code{"9"}. If there are two -strings where one is a prefix of the other, the shorter string is less than -the longer one. Thus @code{"abc"} is less than @code{"abcd"}.@refill - -Here are some sample expressions, how @code{gawk} compares them, and what -the result of the comparison is. - -@table @code -@item 1.5 <= 2.0 -numeric comparison (true) - -@item "abc" >= "xyz" -string comparison (false) - -@item 1.5 != " +2" -string comparison (true) - -@item "1e2" < "3" -string comparison (true) - -@item a = 2; b = "2" -@itemx a == b -string comparison (true) -@end table - -@example -echo 1e2 3 | awk '@{ print ($1 < $2) ? "true" : "false" @}' -@end example - -@noindent -prints @samp{false} since both @code{$1} and @code{$2} are numeric -strings and thus have both string and numeric types, thus dictating -a numeric comparison. - -The purpose of the comparison rules and the use of numeric strings is -to attempt to produce the behavior that is ``least surprising,'' while -still ``doing the right thing.'' - -String comparisons and regular expression comparisons are very different. -For example, - -@example -$1 == "foo" -@end example - -@noindent -has the value of 1, or is true, if the first field of the current input -record is precisely @samp{foo}. By contrast, - -@example -$1 ~ /foo/ -@end example - -@noindent -has the value 1 if the first field contains @samp{foo}, such as @samp{foobar}. - -The right hand operand of the @samp{~} and @samp{!~} operators may be -either a constant regexp (@code{/@dots{}/}), or it may be an ordinary -expression, in which case the value of the expression as a string is a -dynamic regexp (@pxref{Regexp Usage, ,How to Use Regular Expressions}). - -@cindex regexp as expression -In very recent implementations of @code{awk}, a constant regular -expression in slashes by itself is also an expression. The regexp -@code{/@var{regexp}/} is an abbreviation for this comparison expression: - -@example -$0 ~ /@var{regexp}/ -@end example - -In some contexts it may be necessary to write parentheses around the -regexp to avoid confusing the @code{gawk} parser. For example, -@code{(/x/ - /y/) > threshold} is not allowed, but @code{((/x/) - (/y/)) -> threshold} parses properly. - -One special place where @code{/foo/} is @emph{not} an abbreviation for -@code{$0 ~ /foo/} is when it is the right-hand operand of @samp{~} or -@samp{!~}! @xref{Constants, ,Constant Expressions}, where this is -discussed in more detail. - -@node Boolean Ops, Assignment Ops, Comparison Ops, Expressions -@section Boolean Expressions -@cindex expressions, boolean -@cindex boolean expressions -@cindex operators, boolean -@cindex boolean operators -@cindex logical operations -@cindex and operator -@cindex or operator -@cindex not operator - -A @dfn{boolean expression} is a combination of comparison expressions or -matching expressions, using the boolean operators ``or'' -(@samp{||}), ``and'' (@samp{&&}), and ``not'' (@samp{!}), along with -parentheses to control nesting. The truth of the boolean expression is -computed by combining the truth values of the component expressions. - -Boolean expressions can be used wherever comparison and matching -expressions can be used. They can be used in @code{if}, @code{while} -@code{do} and @code{for} statements. They have numeric values (1 if true, -0 if false), which come into play if the result of the boolean expression -is stored in a variable, or used in arithmetic.@refill - -In addition, every boolean expression is also a valid boolean pattern, so -you can use it as a pattern to control the execution of rules. - -Here are descriptions of the three boolean operators, with an example of -each. It may be instructive to compare these examples with the -analogous examples of boolean patterns -(@pxref{Boolean Patterns, ,Boolean Operators and Patterns}), which -use the same boolean operators in patterns instead of expressions.@refill - -@table @code -@item @var{boolean1} && @var{boolean2} -True if both @var{boolean1} and @var{boolean2} are true. For example, -the following statement prints the current input record if it contains -both @samp{2400} and @samp{foo}.@refill - -@smallexample -if ($0 ~ /2400/ && $0 ~ /foo/) print -@end smallexample - -The subexpression @var{boolean2} is evaluated only if @var{boolean1} -is true. This can make a difference when @var{boolean2} contains -expressions that have side effects: in the case of @code{$0 ~ /foo/ && -($2 == bar++)}, the variable @code{bar} is not incremented if there is -no @samp{foo} in the record. - -@item @var{boolean1} || @var{boolean2} -True if at least one of @var{boolean1} or @var{boolean2} is true. -For example, the following command prints all records in the input -file @file{BBS-list} that contain @emph{either} @samp{2400} or -@samp{foo}, or both.@refill - -@smallexample -awk '@{ if ($0 ~ /2400/ || $0 ~ /foo/) print @}' BBS-list -@end smallexample - -The subexpression @var{boolean2} is evaluated only if @var{boolean1} -is false. This can make a difference when @var{boolean2} contains -expressions that have side effects. - -@item !@var{boolean} -True if @var{boolean} is false. For example, the following program prints -all records in the input file @file{BBS-list} that do @emph{not} contain the -string @samp{foo}. - -@smallexample -awk '@{ if (! ($0 ~ /foo/)) print @}' BBS-list -@end smallexample -@end table - -@node Assignment Ops, Increment Ops, Boolean Ops, Expressions -@section Assignment Expressions -@cindex assignment operators -@cindex operators, assignment -@cindex expressions, assignment - -An @dfn{assignment} is an expression that stores a new value into a -variable. For example, let's assign the value 1 to the variable -@code{z}:@refill - -@example -z = 1 -@end example - -After this expression is executed, the variable @code{z} has the value 1. -Whatever old value @code{z} had before the assignment is forgotten. - -Assignments can store string values also. For example, this would store -the value @code{"this food is good"} in the variable @code{message}: - -@example -thing = "food" -predicate = "good" -message = "this " thing " is " predicate -@end example - -@noindent -(This also illustrates concatenation of strings.) - -The @samp{=} sign is called an @dfn{assignment operator}. It is the -simplest assignment operator because the value of the right-hand -operand is stored unchanged. - -@cindex side effect -Most operators (addition, concatenation, and so on) have no effect -except to compute a value. If you ignore the value, you might as well -not use the operator. An assignment operator is different; it does -produce a value, but even if you ignore the value, the assignment still -makes itself felt through the alteration of the variable. We call this -a @dfn{side effect}. - -@cindex lvalue -The left-hand operand of an assignment need not be a variable -(@pxref{Variables}); it can also be a field -(@pxref{Changing Fields, ,Changing the Contents of a Field}) or -an array element (@pxref{Arrays, ,Arrays in @code{awk}}). -These are all called @dfn{lvalues}, -which means they can appear on the left-hand side of an assignment operator. -The right-hand operand may be any expression; it produces the new value -which the assignment stores in the specified variable, field or array -element.@refill - -It is important to note that variables do @emph{not} have permanent types. -The type of a variable is simply the type of whatever value it happens -to hold at the moment. In the following program fragment, the variable -@code{foo} has a numeric value at first, and a string value later on: - -@example -foo = 1 -print foo -foo = "bar" -print foo -@end example - -@noindent -When the second assignment gives @code{foo} a string value, the fact that -it previously had a numeric value is forgotten. - -An assignment is an expression, so it has a value: the same value that -is assigned. Thus, @code{z = 1} as an expression has the value 1. -One consequence of this is that you can write multiple assignments together: - -@example -x = y = z = 0 -@end example - -@noindent -stores the value 0 in all three variables. It does this because the -value of @code{z = 0}, which is 0, is stored into @code{y}, and then -the value of @code{y = z = 0}, which is 0, is stored into @code{x}. - -You can use an assignment anywhere an expression is called for. For -example, it is valid to write @code{x != (y = 1)} to set @code{y} to 1 -and then test whether @code{x} equals 1. But this style tends to make -programs hard to read; except in a one-shot program, you should -rewrite it to get rid of such nesting of assignments. This is never very -hard. - -Aside from @samp{=}, there are several other assignment operators that -do arithmetic with the old value of the variable. For example, the -operator @samp{+=} computes a new value by adding the right-hand value -to the old value of the variable. Thus, the following assignment adds -5 to the value of @code{foo}: - -@example -foo += 5 -@end example - -@noindent -This is precisely equivalent to the following: - -@example -foo = foo + 5 -@end example - -@noindent -Use whichever one makes the meaning of your program clearer. - -Here is a table of the arithmetic assignment operators. In each -case, the right-hand operand is an expression whose value is converted -to a number. - -@table @code -@item @var{lvalue} += @var{increment} -Adds @var{increment} to the value of @var{lvalue} to make the new value -of @var{lvalue}. - -@item @var{lvalue} -= @var{decrement} -Subtracts @var{decrement} from the value of @var{lvalue}. - -@item @var{lvalue} *= @var{coefficient} -Multiplies the value of @var{lvalue} by @var{coefficient}. - -@item @var{lvalue} /= @var{quotient} -Divides the value of @var{lvalue} by @var{quotient}. - -@item @var{lvalue} %= @var{modulus} -Sets @var{lvalue} to its remainder by @var{modulus}. - -@item @var{lvalue} ^= @var{power} -@itemx @var{lvalue} **= @var{power} -Raises @var{lvalue} to the power @var{power}. -(Only the @code{^=} operator is specified by @sc{posix}.) -@end table - -@ignore -From: gatech!ames!elroy!cit-vax!EQL.Caltech.Edu!rankin (Pat Rankin) - In the discussion of assignment operators, it states that -``foo += 5'' "is precisely equivalent to" ``foo = foo + 5'' (p.77). That -may be true for simple variables, but it's not true for expressions with -side effects, like array references. For proof, try - BEGIN { - foo[rand()] += 5; for (x in foo) print x, foo[x] - bar[rand()] = bar[rand()] + 5; for (x in bar) print x, bar[x] - } -I suspect that the original statement is simply untrue--that '+=' is more -efficient in all cases. - -ADR --- Try to add something about this here for the next go 'round. -@end ignore - -@node Increment Ops, Conversion, Assignment Ops, Expressions -@section Increment Operators - -@cindex increment operators -@cindex operators, increment -@dfn{Increment operators} increase or decrease the value of a variable -by 1. You could do the same thing with an assignment operator, so -the increment operators add no power to the @code{awk} language; but they -are convenient abbreviations for something very common. - -The operator to add 1 is written @samp{++}. It can be used to increment -a variable either before or after taking its value. - -To pre-increment a variable @var{v}, write @code{++@var{v}}. This adds -1 to the value of @var{v} and that new value is also the value of this -expression. The assignment expression @code{@var{v} += 1} is completely -equivalent. - -Writing the @samp{++} after the variable specifies post-increment. This -increments the variable value just the same; the difference is that the -value of the increment expression itself is the variable's @emph{old} -value. Thus, if @code{foo} has the value 4, then the expression @code{foo++} -has the value 4, but it changes the value of @code{foo} to 5. - -The post-increment @code{foo++} is nearly equivalent to writing @code{(foo -+= 1) - 1}. It is not perfectly equivalent because all numbers in -@code{awk} are floating point: in floating point, @code{foo + 1 - 1} does -not necessarily equal @code{foo}. But the difference is minute as -long as you stick to numbers that are fairly small (less than a trillion). - -Any lvalue can be incremented. Fields and array elements are incremented -just like variables. (Use @samp{$(i++)} when you wish to do a field reference -and a variable increment at the same time. The parentheses are necessary -because of the precedence of the field reference operator, @samp{$}.) -@c expert information in the last parenthetical remark - -The decrement operator @samp{--} works just like @samp{++} except that -it subtracts 1 instead of adding. Like @samp{++}, it can be used before -the lvalue to pre-decrement or after it to post-decrement. - -Here is a summary of increment and decrement expressions. - -@table @code -@item ++@var{lvalue} -This expression increments @var{lvalue} and the new value becomes the -value of this expression. - -@item @var{lvalue}++ -This expression causes the contents of @var{lvalue} to be incremented. -The value of the expression is the @emph{old} value of @var{lvalue}. - -@item --@var{lvalue} -Like @code{++@var{lvalue}}, but instead of adding, it subtracts. It -decrements @var{lvalue} and delivers the value that results. - -@item @var{lvalue}-- -Like @code{@var{lvalue}++}, but instead of adding, it subtracts. It -decrements @var{lvalue}. The value of the expression is the @emph{old} -value of @var{lvalue}. -@end table - -@node Conversion, Values, Increment Ops, Expressions -@section Conversion of Strings and Numbers - -@cindex conversion of strings and numbers -Strings are converted to numbers, and numbers to strings, if the context -of the @code{awk} program demands it. For example, if the value of -either @code{foo} or @code{bar} in the expression @code{foo + bar} -happens to be a string, it is converted to a number before the addition -is performed. If numeric values appear in string concatenation, they -are converted to strings. Consider this:@refill - -@example -two = 2; three = 3 -print (two three) + 4 -@end example - -@noindent -This eventually prints the (numeric) value 27. The numeric values of -the variables @code{two} and @code{three} are converted to strings and -concatenated together, and the resulting string is converted back to the -number 23, to which 4 is then added. - -If, for some reason, you need to force a number to be converted to a -string, concatenate the null string with that number. To force a string -to be converted to a number, add zero to that string. - -A string is converted to a number by interpreting a numeric prefix -of the string as numerals: -@code{"2.5"} converts to 2.5, @code{"1e3"} converts to 1000, and @code{"25fix"} -has a numeric value of 25. -Strings that can't be interpreted as valid numbers are converted to -zero. - -@vindex CONVFMT -The exact manner in which numbers are converted into strings is controlled -by the @code{awk} built-in variable @code{CONVFMT} (@pxref{Built-in Variables}). -Numbers are converted using a special version of the @code{sprintf} function -(@pxref{Built-in, ,Built-in Functions}) with @code{CONVFMT} as the format -specifier.@refill - -@code{CONVFMT}'s default value is @code{"%.6g"}, which prints a value with -at least six significant digits. For some applications you will want to -change it to specify more precision. Double precision on most modern -machines gives you 16 or 17 decimal digits of precision. - -Strange results can happen if you set @code{CONVFMT} to a string that doesn't -tell @code{sprintf} how to format floating point numbers in a useful way. -For example, if you forget the @samp{%} in the format, all numbers will be -converted to the same constant string.@refill - -As a special case, if a number is an integer, then the result of converting -it to a string is @emph{always} an integer, no matter what the value of -@code{CONVFMT} may be. Given the following code fragment: - -@example -CONVFMT = "%2.2f" -a = 12 -b = a "" -@end example - -@noindent -@code{b} has the value @code{"12"}, not @code{"12.00"}. - -@ignore -For the 2.14 version, describe the ``stickyness'' of conversions. Right now -the manual assumes everywhere that variables are either numbers or strings; -in fact both kinds of values may be valid. If both happen to be valid, a -conversion isn't necessary and isn't done. Revising the manual to be -consistent with this, though, is too big a job to tackle at the moment. - -7/92: This has sort of been done, only the section isn't completely right! - What to do? -7/92: Pretty much fixed, at least for the short term, thanks to text - from David. -@end ignore - -@vindex OFMT -Prior to the @sc{posix} standard, @code{awk} specified that the value -of @code{OFMT} was used for converting numbers to strings. @code{OFMT} -specifies the output format to use when printing numbers with @code{print}. -@code{CONVFMT} was introduced in order to separate the semantics of -conversions from the semantics of printing. Both @code{CONVFMT} and -@code{OFMT} have the same default value: @code{"%.6g"}. In the vast majority -of cases, old @code{awk} programs will not change their behavior. -However, this use of @code{OFMT} is something to keep in mind if you must -port your program to other implementations of @code{awk}; we recommend -that instead of changing your programs, you just port @code{gawk} itself!@refill - -@node Values, Conditional Exp, Conversion, Expressions -@section Numeric and String Values -@cindex conversion of strings and numbers - -Through most of this manual, we present @code{awk} values (such as constants, -fields, or variables) as @emph{either} numbers @emph{or} strings. This is -a convenient way to think about them, since typically they are used in only -one way, or the other. - -In truth though, @code{awk} values can be @emph{both} string and -numeric, at the same time. Internally, @code{awk} represents values -with a string, a (floating point) number, and an indication that one, -the other, or both representations of the value are valid. - -Keeping track of both kinds of values is important for execution -efficiency: a variable can acquire a string value the first time it -is used as a string, and then that string value can be used until the -variable is assigned a new value. Thus, if a variable with only a numeric -value is used in several concatenations in a row, it only has to be given -a string representation once. The numeric value remains valid, so that -no conversion back to a number is necessary if the variable is later used -in an arithmetic expression. - -Tracking both kinds of values is also important for precise numerical -calculations. Consider the following: - -@smallexample -a = 123.321 -CONVFMT = "%3.1f" -b = a " is a number" -c = a + 1.654 -@end smallexample - -@noindent -The variable @code{a} receives a string value in the concatenation and -assignment to @code{b}. The string value of @code{a} is @code{"123.3"}. -If the numeric value was lost when it was converted to a string, then the -numeric use of @code{a} in the last statement would lose information. -@code{c} would be assigned the value 124.954 instead of 124.975. -Such errors accumulate rapidly, and very adversely affect numeric -computations.@refill - -Once a numeric value acquires a corresponding string value, it stays valid -until a new assignment is made. If @code{CONVFMT} -(@pxref{Conversion, ,Conversion of Strings and Numbers}) changes in the -meantime, the old string value will still be used. For example:@refill - -@smallexample -BEGIN @{ - CONVFMT = "%2.2f" - a = 123.456 - b = a "" # force `a' to have string value too - printf "a = %s\n", a - CONVFMT = "%.6g" - printf "a = %s\n", a - a += 0 # make `a' numeric only again - printf "a = %s\n", a # use `a' as string -@} -@end smallexample - -@noindent -This program prints @samp{a = 123.46} twice, and then prints -@samp{a = 123.456}. - -@xref{Conversion, ,Conversion of Strings and Numbers}, for the rules that -specify how string values are made from numeric values. - -@node Conditional Exp, Function Calls, Values, Expressions -@section Conditional Expressions -@cindex conditional expression -@cindex expression, conditional - -A @dfn{conditional expression} is a special kind of expression with -three operands. It allows you to use one expression's value to select -one of two other expressions. - -The conditional expression looks the same as in the C language: - -@example -@var{selector} ? @var{if-true-exp} : @var{if-false-exp} -@end example - -@noindent -There are three subexpressions. The first, @var{selector}, is always -computed first. If it is ``true'' (not zero and not null) then -@var{if-true-exp} is computed next and its value becomes the value of -the whole expression. Otherwise, @var{if-false-exp} is computed next -and its value becomes the value of the whole expression.@refill - -For example, this expression produces the absolute value of @code{x}: - -@example -x > 0 ? x : -x -@end example - -Each time the conditional expression is computed, exactly one of -@var{if-true-exp} and @var{if-false-exp} is computed; the other is ignored. -This is important when the expressions contain side effects. For example, -this conditional expression examines element @code{i} of either array -@code{a} or array @code{b}, and increments @code{i}. - -@example -x == y ? a[i++] : b[i++] -@end example - -@noindent -This is guaranteed to increment @code{i} exactly once, because each time -one or the other of the two increment expressions is executed, -and the other is not. - -@node Function Calls, Precedence, Conditional Exp, Expressions -@section Function Calls -@cindex function call -@cindex calling a function - -A @dfn{function} is a name for a particular calculation. Because it has -a name, you can ask for it by name at any point in the program. For -example, the function @code{sqrt} computes the square root of a number. - -A fixed set of functions are @dfn{built-in}, which means they are -available in every @code{awk} program. The @code{sqrt} function is one -of these. @xref{Built-in, ,Built-in Functions}, for a list of built-in -functions and their descriptions. In addition, you can define your own -functions in the program for use elsewhere in the same program. -@xref{User-defined, ,User-defined Functions}, for how to do this.@refill - -@cindex arguments in function call -The way to use a function is with a @dfn{function call} expression, -which consists of the function name followed by a list of -@dfn{arguments} in parentheses. The arguments are expressions which -give the raw materials for the calculation that the function will do. -When there is more than one argument, they are separated by commas. If -there are no arguments, write just @samp{()} after the function name. -Here are some examples: - -@example -sqrt(x^2 + y^2) # @r{One argument} -atan2(y, x) # @r{Two arguments} -rand() # @r{No arguments} -@end example - -@strong{Do not put any space between the function name and the -open-parenthesis!} A user-defined function name looks just like the name of -a variable, and space would make the expression look like concatenation -of a variable with an expression inside parentheses. Space before the -parenthesis is harmless with built-in functions, but it is best not to get -into the habit of using space to avoid mistakes with user-defined -functions. - -Each function expects a particular number of arguments. For example, the -@code{sqrt} function must be called with a single argument, the number -to take the square root of: - -@example -sqrt(@var{argument}) -@end example - -Some of the built-in functions allow you to omit the final argument. -If you do so, they use a reasonable default. -@xref{Built-in, ,Built-in Functions}, for full details. If arguments -are omitted in calls to user-defined functions, then those arguments are -treated as local variables, initialized to the null string -(@pxref{User-defined, ,User-defined Functions}).@refill - -Like every other expression, the function call has a value, which is -computed by the function based on the arguments you give it. In this -example, the value of @code{sqrt(@var{argument})} is the square root of the -argument. A function can also have side effects, such as assigning the -values of certain variables or doing I/O. - -Here is a command to read numbers, one number per line, and print the -square root of each one: - -@example -awk '@{ print "The square root of", $1, "is", sqrt($1) @}' -@end example - -@node Precedence, , Function Calls, Expressions -@section Operator Precedence (How Operators Nest) -@cindex precedence -@cindex operator precedence - -@dfn{Operator precedence} determines how operators are grouped, when -different operators appear close by in one expression. For example, -@samp{*} has higher precedence than @samp{+}; thus, @code{a + b * c} -means to multiply @code{b} and @code{c}, and then add @code{a} to the -product (i.e., @code{a + (b * c)}). - -You can overrule the precedence of the operators by using parentheses. -You can think of the precedence rules as saying where the -parentheses are assumed if you do not write parentheses yourself. In -fact, it is wise to always use parentheses whenever you have an unusual -combination of operators, because other people who read the program may -not remember what the precedence is in this case. You might forget, -too; then you could make a mistake. Explicit parentheses will help prevent -any such mistake. - -When operators of equal precedence are used together, the leftmost -operator groups first, except for the assignment, conditional and -exponentiation operators, which group in the opposite order. -Thus, @code{a - b + c} groups as @code{(a - b) + c}; -@code{a = b = c} groups as @code{a = (b = c)}.@refill - -The precedence of prefix unary operators does not matter as long as only -unary operators are involved, because there is only one way to parse -them---innermost first. Thus, @code{$++i} means @code{$(++i)} and -@code{++$x} means @code{++($x)}. However, when another operator follows -the operand, then the precedence of the unary operators can matter. -Thus, @code{$x^2} means @code{($x)^2}, but @code{-x^2} means -@code{-(x^2)}, because @samp{-} has lower precedence than @samp{^} -while @samp{$} has higher precedence. - -Here is a table of the operators of @code{awk}, in order of increasing -precedence: - -@table @asis -@item assignment -@samp{=}, @samp{+=}, @samp{-=}, @samp{*=}, @samp{/=}, @samp{%=}, -@samp{^=}, @samp{**=}. These operators group right-to-left. -(The @samp{**=} operator is not specified by @sc{posix}.) - -@item conditional -@samp{?:}. This operator groups right-to-left. - -@item logical ``or''. -@samp{||}. - -@item logical ``and''. -@samp{&&}. - -@item array membership -@samp{in}. - -@item matching -@samp{~}, @samp{!~}. - -@item relational, and redirection -The relational operators and the redirections have the same precedence -level. Characters such as @samp{>} serve both as relationals and as -redirections; the context distinguishes between the two meanings. - -The relational operators are @samp{<}, @samp{<=}, @samp{==}, @samp{!=}, -@samp{>=} and @samp{>}. - -The I/O redirection operators are @samp{<}, @samp{>}, @samp{>>} and -@samp{|}. - -Note that I/O redirection operators in @code{print} and @code{printf} -statements belong to the statement level, not to expressions. The -redirection does not produce an expression which could be the operand of -another operator. As a result, it does not make sense to use a -redirection operator near another operator of lower precedence, without -parentheses. Such combinations, for example @samp{print foo > a ? b : -c}, result in syntax errors. - -@item concatenation -No special token is used to indicate concatenation. -The operands are simply written side by side. - -@item add, subtract -@samp{+}, @samp{-}. - -@item multiply, divide, mod -@samp{*}, @samp{/}, @samp{%}. - -@item unary plus, minus, ``not'' -@samp{+}, @samp{-}, @samp{!}. - -@item exponentiation -@samp{^}, @samp{**}. These operators group right-to-left. -(The @samp{**} operator is not specified by @sc{posix}.) - -@item increment, decrement -@samp{++}, @samp{--}. - -@item field -@samp{$}. -@end table - -@node Statements, Arrays, Expressions, Top -@chapter Control Statements in Actions -@cindex control statement - -@dfn{Control statements} such as @code{if}, @code{while}, and so on -control the flow of execution in @code{awk} programs. Most of the -control statements in @code{awk} are patterned on similar statements in -C. - -All the control statements start with special keywords such as @code{if} -and @code{while}, to distinguish them from simple expressions. - -Many control statements contain other statements; for example, the -@code{if} statement contains another statement which may or may not be -executed. The contained statement is called the @dfn{body}. If you -want to include more than one statement in the body, group them into a -single compound statement with curly braces, separating them with -newlines or semicolons. - -@menu -* If Statement:: Conditionally execute - some @code{awk} statements. -* While Statement:: Loop until some condition is satisfied. -* Do Statement:: Do specified action while looping until some - condition is satisfied. -* For Statement:: Another looping statement, that provides - initialization and increment clauses. -* Break Statement:: Immediately exit the innermost enclosing loop. -* Continue Statement:: Skip to the end of the innermost - enclosing loop. -* Next Statement:: Stop processing the current input record. -* Next File Statement:: Stop processing the current file. -* Exit Statement:: Stop execution of @code{awk}. -@end menu - -@node If Statement, While Statement, Statements, Statements -@section The @code{if} Statement - -@cindex @code{if} statement -The @code{if}-@code{else} statement is @code{awk}'s decision-making -statement. It looks like this:@refill - -@example -if (@var{condition}) @var{then-body} @r{[}else @var{else-body}@r{]} -@end example - -@noindent -@var{condition} is an expression that controls what the rest of the -statement will do. If @var{condition} is true, @var{then-body} is -executed; otherwise, @var{else-body} is executed (assuming that the -@code{else} clause is present). The @code{else} part of the statement is -optional. The condition is considered false if its value is zero or -the null string, and true otherwise.@refill - -Here is an example: - -@example -if (x % 2 == 0) - print "x is even" -else - print "x is odd" -@end example - -In this example, if the expression @code{x % 2 == 0} is true (that is, -the value of @code{x} is divisible by 2), then the first @code{print} -statement is executed, otherwise the second @code{print} statement is -performed.@refill - -If the @code{else} appears on the same line as @var{then-body}, and -@var{then-body} is not a compound statement (i.e., not surrounded by -curly braces), then a semicolon must separate @var{then-body} from -@code{else}. To illustrate this, let's rewrite the previous example: - -@example -awk '@{ if (x % 2 == 0) print "x is even"; else - print "x is odd" @}' -@end example - -@noindent -If you forget the @samp{;}, @code{awk} won't be able to parse the -statement, and you will get a syntax error. - -We would not actually write this example this way, because a human -reader might fail to see the @code{else} if it were not the first thing -on its line. - -@node While Statement, Do Statement, If Statement, Statements -@section The @code{while} Statement -@cindex @code{while} statement -@cindex loop -@cindex body of a loop - -In programming, a @dfn{loop} means a part of a program that is (or at least can -be) executed two or more times in succession. - -The @code{while} statement is the simplest looping statement in -@code{awk}. It repeatedly executes a statement as long as a condition is -true. It looks like this: - -@example -while (@var{condition}) - @var{body} -@end example - -@noindent -Here @var{body} is a statement that we call the @dfn{body} of the loop, -and @var{condition} is an expression that controls how long the loop -keeps running. - -The first thing the @code{while} statement does is test @var{condition}. -If @var{condition} is true, it executes the statement @var{body}. -(@var{condition} is true when the value -is not zero and not a null string.) After @var{body} has been executed, -@var{condition} is tested again, and if it is still true, @var{body} is -executed again. This process repeats until @var{condition} is no longer -true. If @var{condition} is initially false, the body of the loop is -never executed.@refill - -This example prints the first three fields of each record, one per line. - -@example -awk '@{ i = 1 - while (i <= 3) @{ - print $i - i++ - @} -@}' -@end example - -@noindent -Here the body of the loop is a compound statement enclosed in braces, -containing two statements. - -The loop works like this: first, the value of @code{i} is set to 1. -Then, the @code{while} tests whether @code{i} is less than or equal to -three. This is the case when @code{i} equals one, so the @code{i}-th -field is printed. Then the @code{i++} increments the value of @code{i} -and the loop repeats. The loop terminates when @code{i} reaches 4. - -As you can see, a newline is not required between the condition and the -body; but using one makes the program clearer unless the body is a -compound statement or is very simple. The newline after the open-brace -that begins the compound statement is not required either, but the -program would be hard to read without it. - -@node Do Statement, For Statement, While Statement, Statements -@section The @code{do}-@code{while} Statement - -The @code{do} loop is a variation of the @code{while} looping statement. -The @code{do} loop executes the @var{body} once, then repeats @var{body} -as long as @var{condition} is true. It looks like this: - -@example -do - @var{body} -while (@var{condition}) -@end example - -Even if @var{condition} is false at the start, @var{body} is executed at -least once (and only once, unless executing @var{body} makes -@var{condition} true). Contrast this with the corresponding -@code{while} statement: - -@example -while (@var{condition}) - @var{body} -@end example - -@noindent -This statement does not execute @var{body} even once if @var{condition} -is false to begin with. - -Here is an example of a @code{do} statement: - -@example -awk '@{ i = 1 - do @{ - print $0 - i++ - @} while (i <= 10) -@}' -@end example - -@noindent -prints each input record ten times. It isn't a very realistic example, -since in this case an ordinary @code{while} would do just as well. But -this reflects actual experience; there is only occasionally a real use -for a @code{do} statement.@refill - -@node For Statement, Break Statement, Do Statement, Statements -@section The @code{for} Statement -@cindex @code{for} statement - -The @code{for} statement makes it more convenient to count iterations of a -loop. The general form of the @code{for} statement looks like this:@refill - -@example -for (@var{initialization}; @var{condition}; @var{increment}) - @var{body} -@end example - -@noindent -This statement starts by executing @var{initialization}. Then, as long -as @var{condition} is true, it repeatedly executes @var{body} and then -@var{increment}. Typically @var{initialization} sets a variable to -either zero or one, @var{increment} adds 1 to it, and @var{condition} -compares it against the desired number of iterations. - -Here is an example of a @code{for} statement: - -@example -@group -awk '@{ for (i = 1; i <= 3; i++) - print $i -@}' -@end group -@end example - -@noindent -This prints the first three fields of each input record, one field per -line. - -In the @code{for} statement, @var{body} stands for any statement, but -@var{initialization}, @var{condition} and @var{increment} are just -expressions. You cannot set more than one variable in the -@var{initialization} part unless you use a multiple assignment statement -such as @code{x = y = 0}, which is possible only if all the initial values -are equal. (But you can initialize additional variables by writing -their assignments as separate statements preceding the @code{for} loop.) - -The same is true of the @var{increment} part; to increment additional -variables, you must write separate statements at the end of the loop. -The C compound expression, using C's comma operator, would be useful in -this context, but it is not supported in @code{awk}. - -Most often, @var{increment} is an increment expression, as in the -example above. But this is not required; it can be any expression -whatever. For example, this statement prints all the powers of 2 -between 1 and 100: - -@example -for (i = 1; i <= 100; i *= 2) - print i -@end example - -Any of the three expressions in the parentheses following the @code{for} may -be omitted if there is nothing to be done there. Thus, @w{@samp{for (;x -> 0;)}} is equivalent to @w{@samp{while (x > 0)}}. If the -@var{condition} is omitted, it is treated as @var{true}, effectively -yielding an @dfn{infinite loop} (i.e., a loop that will never -terminate).@refill - -In most cases, a @code{for} loop is an abbreviation for a @code{while} -loop, as shown here: - -@example -@var{initialization} -while (@var{condition}) @{ - @var{body} - @var{increment} -@} -@end example - -@noindent -The only exception is when the @code{continue} statement -(@pxref{Continue Statement, ,The @code{continue} Statement}) is used -inside the loop; changing a @code{for} statement to a @code{while} -statement in this way can change the effect of the @code{continue} -statement inside the loop.@refill - -There is an alternate version of the @code{for} loop, for iterating over -all the indices of an array: - -@example -for (i in array) - @var{do something with} array[i] -@end example - -@noindent -@xref{Arrays, ,Arrays in @code{awk}}, for more information on this -version of the @code{for} loop. - -The @code{awk} language has a @code{for} statement in addition to a -@code{while} statement because often a @code{for} loop is both less work to -type and more natural to think of. Counting the number of iterations is -very common in loops. It can be easier to think of this counting as part -of looping rather than as something to do inside the loop. - -The next section has more complicated examples of @code{for} loops. - -@node Break Statement, Continue Statement, For Statement, Statements -@section The @code{break} Statement -@cindex @code{break} statement -@cindex loops, exiting - -The @code{break} statement jumps out of the innermost @code{for}, -@code{while}, or @code{do}-@code{while} loop that encloses it. The -following example finds the smallest divisor of any integer, and also -identifies prime numbers:@refill - -@smallexample -awk '# find smallest divisor of num - @{ num = $1 - for (div = 2; div*div <= num; div++) - if (num % div == 0) - break - if (num % div == 0) - printf "Smallest divisor of %d is %d\n", num, div - else - printf "%d is prime\n", num @}' -@end smallexample - -When the remainder is zero in the first @code{if} statement, @code{awk} -immediately @dfn{breaks out} of the containing @code{for} loop. This means -that @code{awk} proceeds immediately to the statement following the loop -and continues processing. (This is very different from the @code{exit} -statement which stops the entire @code{awk} program. -@xref{Exit Statement, ,The @code{exit} Statement}.)@refill - -Here is another program equivalent to the previous one. It illustrates how -the @var{condition} of a @code{for} or @code{while} could just as well be -replaced with a @code{break} inside an @code{if}: - -@smallexample -@group -awk '# find smallest divisor of num - @{ num = $1 - for (div = 2; ; div++) @{ - if (num % div == 0) @{ - printf "Smallest divisor of %d is %d\n", num, div - break - @} - if (div*div > num) @{ - printf "%d is prime\n", num - break - @} - @} -@}' -@end group -@end smallexample - -@node Continue Statement, Next Statement, Break Statement, Statements -@section The @code{continue} Statement - -@cindex @code{continue} statement -The @code{continue} statement, like @code{break}, is used only inside -@code{for}, @code{while}, and @code{do}-@code{while} loops. It skips -over the rest of the loop body, causing the next cycle around the loop -to begin immediately. Contrast this with @code{break}, which jumps out -of the loop altogether. Here is an example:@refill - -@example -# print names that don't contain the string "ignore" - -# first, save the text of each line -@{ names[NR] = $0 @} - -# print what we're interested in -END @{ - for (x in names) @{ - if (names[x] ~ /ignore/) - continue - print names[x] - @} -@} -@end example - -If one of the input records contains the string @samp{ignore}, this -example skips the print statement for that record, and continues back to -the first statement in the loop. - -This is not a practical example of @code{continue}, since it would be -just as easy to write the loop like this: - -@example -for (x in names) - if (names[x] !~ /ignore/) - print names[x] -@end example - -@ignore -from brennan@boeing.com: - -page 90, section 9.6. The example is too artificial as -the one line program - - !/ignore/ - -does the same thing. -@end ignore -@c ADR --- he's right, but don't worry about this for now - -The @code{continue} statement in a @code{for} loop directs @code{awk} to -skip the rest of the body of the loop, and resume execution with the -increment-expression of the @code{for} statement. The following program -illustrates this fact:@refill - -@example -awk 'BEGIN @{ - for (x = 0; x <= 20; x++) @{ - if (x == 5) - continue - printf ("%d ", x) - @} - print "" -@}' -@end example - -@noindent -This program prints all the numbers from 0 to 20, except for 5, for -which the @code{printf} is skipped. Since the increment @code{x++} -is not skipped, @code{x} does not remain stuck at 5. Contrast the -@code{for} loop above with the @code{while} loop: - -@example -awk 'BEGIN @{ - x = 0 - while (x <= 20) @{ - if (x == 5) - continue - printf ("%d ", x) - x++ - @} - print "" -@}' -@end example - -@noindent -This program loops forever once @code{x} gets to 5. - -As described above, the @code{continue} statement has no meaning when -used outside the body of a loop. However, although it was never documented, -historical implementations of @code{awk} have treated the @code{continue} -statement outside of a loop as if it were a @code{next} statement -(@pxref{Next Statement, ,The @code{next} Statement}). -By default, @code{gawk} silently supports this usage. However, if -@samp{-W posix} has been specified on the command line -(@pxref{Command Line, ,Invoking @code{awk}}), -it will be treated as an error, since the @sc{posix} standard specifies -that @code{continue} should only be used inside the body of a loop.@refill - -@node Next Statement, Next File Statement, Continue Statement, Statements -@section The @code{next} Statement -@cindex @code{next} statement - -The @code{next} statement forces @code{awk} to immediately stop processing -the current record and go on to the next record. This means that no -further rules are executed for the current record. The rest of the -current rule's action is not executed either. - -Contrast this with the effect of the @code{getline} function -(@pxref{Getline, ,Explicit Input with @code{getline}}). That too causes -@code{awk} to read the next record immediately, but it does not alter the -flow of control in any way. So the rest of the current action executes -with a new input record. - -At the highest level, @code{awk} program execution is a loop that reads -an input record and then tests each rule's pattern against it. If you -think of this loop as a @code{for} statement whose body contains the -rules, then the @code{next} statement is analogous to a @code{continue} -statement: it skips to the end of the body of this implicit loop, and -executes the increment (which reads another record). - -For example, if your @code{awk} program works only on records with four -fields, and you don't want it to fail when given bad input, you might -use this rule near the beginning of the program: - -@smallexample -NF != 4 @{ - printf("line %d skipped: doesn't have 4 fields", FNR) > "/dev/stderr" - next -@} -@end smallexample - -@noindent -so that the following rules will not see the bad record. The error -message is redirected to the standard error output stream, as error -messages should be. @xref{Special Files, ,Standard I/O Streams}. - -According to the @sc{posix} standard, the behavior is undefined if -the @code{next} statement is used in a @code{BEGIN} or @code{END} rule. -@code{gawk} will treat it as a syntax error. - -If the @code{next} statement causes the end of the input to be reached, -then the code in the @code{END} rules, if any, will be executed. -@xref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}. - -@node Next File Statement, Exit Statement, Next Statement, Statements -@section The @code{next file} Statement - -@cindex @code{next file} statement -The @code{next file} statement is similar to the @code{next} statement. -However, instead of abandoning processing of the current record, the -@code{next file} statement instructs @code{awk} to stop processing the -current data file. - -Upon execution of the @code{next file} statement, @code{FILENAME} is -updated to the name of the next data file listed on the command line, -@code{FNR} is reset to 1, and processing starts over with the first -rule in the progam. @xref{Built-in Variables}. - -If the @code{next file} statement causes the end of the input to be reached, -then the code in the @code{END} rules, if any, will be executed. -@xref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}. - -The @code{next file} statement is a @code{gawk} extension; it is not -(currently) available in any other @code{awk} implementation. You can -simulate its behavior by creating a library file named @file{nextfile.awk}, -with the following contents. (This sample program uses user-defined -functions, a feature that has not been presented yet. -@xref{User-defined, ,User-defined Functions}, -for more information.)@refill - -@smallexample -# nextfile --- function to skip remaining records in current file - -# this should be read in before the "main" awk program - -function nextfile() @{ _abandon_ = FILENAME; next @} - -_abandon_ == FILENAME && FNR > 1 @{ next @} -_abandon_ == FILENAME && FNR == 1 @{ _abandon_ = "" @} -@end smallexample - -The @code{nextfile} function simply sets a ``private'' variable@footnote{Since -all variables in @code{awk} are global, this program uses the common -practice of prefixing the variable name with an underscore. In fact, it -also suffixes the variable name with an underscore, as extra insurance -against using a variable name that might be used in some other library -file.} to the name of the current data file, and then retrieves the next -record. Since this file is read before the main @code{awk} program, -the rules that follows the function definition will be executed before the -rules in the main program. The first rule continues to skip records as long as -the name of the input file has not changed, and this is not the first -record in the file. This rule is sufficient most of the time. But what if -the @emph{same} data file is named twice in a row on the command line? -This rule would not process the data file the second time. The second rule -catches this case: If the data file name is what was being skipped, but -@code{FNR} is 1, then this is the second time the file is being processed, -and it should not be skipped. - -The @code{next file} statement would be useful if you have many data -files to process, and due to the nature of the data, you expect that you -would not want to process every record in the file. In order to move on to -the next data file, you would have to continue scanning the unwanted -records (as described above). The @code{next file} statement accomplishes -this much more efficiently. - -@ignore -Would it make sense down the road to nuke `next file' in favor of -semantics that would make this work? - - function nextfile() { ARGIND++ ; next } -@end ignore - -@node Exit Statement, , Next File Statement, Statements -@section The @code{exit} Statement - -@cindex @code{exit} statement -The @code{exit} statement causes @code{awk} to immediately stop -executing the current rule and to stop processing input; any remaining input -is ignored.@refill - -If an @code{exit} statement is executed from a @code{BEGIN} rule the -program stops processing everything immediately. No input records are -read. However, if an @code{END} rule is present, it is executed -(@pxref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}). - -If @code{exit} is used as part of an @code{END} rule, it causes -the program to stop immediately. - -An @code{exit} statement that is part of an ordinary rule (that is, not part -of a @code{BEGIN} or @code{END} rule) stops the execution of any further -automatic rules, but the @code{END} rule is executed if there is one. -If you do not want the @code{END} rule to do its job in this case, you -can set a variable to nonzero before the @code{exit} statement, and check -that variable in the @code{END} rule. - -If an argument is supplied to @code{exit}, its value is used as the exit -status code for the @code{awk} process. If no argument is supplied, -@code{exit} returns status zero (success).@refill - -For example, let's say you've discovered an error condition you really -don't know how to handle. Conventionally, programs report this by -exiting with a nonzero status. Your @code{awk} program can do this -using an @code{exit} statement with a nonzero argument. Here's an -example of this:@refill - -@example -@group -BEGIN @{ - if (("date" | getline date_now) < 0) @{ - print "Can't get system date" > "/dev/stderr" - exit 4 - @} -@} -@end group -@end example - -@node Arrays, Built-in, Statements, Top -@chapter Arrays in @code{awk} - -An @dfn{array} is a table of values, called @dfn{elements}. The -elements of an array are distinguished by their indices. @dfn{Indices} -may be either numbers or strings. Each array has a name, which looks -like a variable name, but must not be in use as a variable name in the -same @code{awk} program. - -@menu -* Array Intro:: Introduction to Arrays -* Reference to Elements:: How to examine one element of an array. -* Assigning Elements:: How to change an element of an array. -* Array Example:: Basic Example of an Array -* Scanning an Array:: A variation of the @code{for} statement. - It loops through the indices of - an array's existing elements. -* Delete:: The @code{delete} statement removes - an element from an array. -* Numeric Array Subscripts:: How to use numbers as subscripts in @code{awk}. -* Multi-dimensional:: Emulating multi-dimensional arrays in @code{awk}. -* Multi-scanning:: Scanning multi-dimensional arrays. -@end menu - -@node Array Intro, Reference to Elements, Arrays, Arrays -@section Introduction to Arrays - -@cindex arrays -The @code{awk} language has one-dimensional @dfn{arrays} for storing groups -of related strings or numbers. - -Every @code{awk} array must have a name. Array names have the same -syntax as variable names; any valid variable name would also be a valid -array name. But you cannot use one name in both ways (as an array and -as a variable) in one @code{awk} program. - -Arrays in @code{awk} superficially resemble arrays in other programming -languages; but there are fundamental differences. In @code{awk}, you -don't need to specify the size of an array before you start to use it. -Additionally, any number or string in @code{awk} may be used as an -array index. - -In most other languages, you have to @dfn{declare} an array and specify -how many elements or components it contains. In such languages, the -declaration causes a contiguous block of memory to be allocated for that -many elements. An index in the array must be a positive integer; for -example, the index 0 specifies the first element in the array, which is -actually stored at the beginning of the block of memory. Index 1 -specifies the second element, which is stored in memory right after the -first element, and so on. It is impossible to add more elements to the -array, because it has room for only as many elements as you declared. - -A contiguous array of four elements might look like this, -conceptually, if the element values are @code{8}, @code{"foo"}, -@code{""} and @code{30}:@refill - -@example -+---------+---------+--------+---------+ -| 8 | "foo" | "" | 30 | @r{value} -+---------+---------+--------+---------+ - 0 1 2 3 @r{index} -@end example - -@noindent -Only the values are stored; the indices are implicit from the order of -the values. @code{8} is the value at index 0, because @code{8} appears in the -position with 0 elements before it. - -@cindex arrays, definition of -@cindex associative arrays -Arrays in @code{awk} are different: they are @dfn{associative}. This means -that each array is a collection of pairs: an index, and its corresponding -array element value: - -@example -@r{Element} 4 @r{Value} 30 -@r{Element} 2 @r{Value} "foo" -@r{Element} 1 @r{Value} 8 -@r{Element} 3 @r{Value} "" -@end example - -@noindent -We have shown the pairs in jumbled order because their order is irrelevant. - -One advantage of an associative array is that new pairs can be added -at any time. For example, suppose we add to the above array a tenth element -whose value is @w{@code{"number ten"}}. The result is this: - -@example -@r{Element} 10 @r{Value} "number ten" -@r{Element} 4 @r{Value} 30 -@r{Element} 2 @r{Value} "foo" -@r{Element} 1 @r{Value} 8 -@r{Element} 3 @r{Value} "" -@end example - -@noindent -Now the array is @dfn{sparse} (i.e., some indices are missing): it has -elements 1--4 and 10, but doesn't have elements 5, 6, 7, 8, or 9.@refill - -Another consequence of associative arrays is that the indices don't -have to be positive integers. Any number, or even a string, can be -an index. For example, here is an array which translates words from -English into French: - -@example -@r{Element} "dog" @r{Value} "chien" -@r{Element} "cat" @r{Value} "chat" -@r{Element} "one" @r{Value} "un" -@r{Element} 1 @r{Value} "un" -@end example - -@noindent -Here we decided to translate the number 1 in both spelled-out and -numeric form---thus illustrating that a single array can have both -numbers and strings as indices. - -When @code{awk} creates an array for you, e.g., with the @code{split} -built-in function, -that array's indices are consecutive integers starting at 1. -(@xref{String Functions, ,Built-in Functions for String Manipulation}.) - -@node Reference to Elements, Assigning Elements, Array Intro, Arrays -@section Referring to an Array Element -@cindex array reference -@cindex element of array -@cindex reference to array - -The principal way of using an array is to refer to one of its elements. -An array reference is an expression which looks like this: - -@example -@var{array}[@var{index}] -@end example - -@noindent -Here, @var{array} is the name of an array. The expression @var{index} is -the index of the element of the array that you want. - -The value of the array reference is the current value of that array -element. For example, @code{foo[4.3]} is an expression for the element -of array @code{foo} at index 4.3. - -If you refer to an array element that has no recorded value, the value -of the reference is @code{""}, the null string. This includes elements -to which you have not assigned any value, and elements that have been -deleted (@pxref{Delete, ,The @code{delete} Statement}). Such a reference -automatically creates that array element, with the null string as its value. -(In some cases, this is unfortunate, because it might waste memory inside -@code{awk}). - -@cindex arrays, presence of elements -You can find out if an element exists in an array at a certain index with -the expression: - -@example -@var{index} in @var{array} -@end example - -@noindent -This expression tests whether or not the particular index exists, -without the side effect of creating that element if it is not present. -The expression has the value 1 (true) if @code{@var{array}[@var{index}]} -exists, and 0 (false) if it does not exist.@refill - -For example, to test whether the array @code{frequencies} contains the -index @code{"2"}, you could write this statement:@refill - -@smallexample -if ("2" in frequencies) print "Subscript \"2\" is present." -@end smallexample - -Note that this is @emph{not} a test of whether or not the array -@code{frequencies} contains an element whose @emph{value} is @code{"2"}. -(There is no way to do that except to scan all the elements.) Also, this -@emph{does not} create @code{frequencies["2"]}, while the following -(incorrect) alternative would do so:@refill - -@smallexample -if (frequencies["2"] != "") print "Subscript \"2\" is present." -@end smallexample - -@node Assigning Elements, Array Example, Reference to Elements, Arrays -@section Assigning Array Elements -@cindex array assignment -@cindex element assignment - -Array elements are lvalues: they can be assigned values just like -@code{awk} variables: - -@example -@var{array}[@var{subscript}] = @var{value} -@end example - -@noindent -Here @var{array} is the name of your array. The expression -@var{subscript} is the index of the element of the array that you want -to assign a value. The expression @var{value} is the value you are -assigning to that element of the array.@refill - -@node Array Example, Scanning an Array, Assigning Elements, Arrays -@section Basic Example of an Array - -The following program takes a list of lines, each beginning with a line -number, and prints them out in order of line number. The line numbers are -not in order, however, when they are first read: they are scrambled. This -program sorts the lines by making an array using the line numbers as -subscripts. It then prints out the lines in sorted order of their numbers. -It is a very simple program, and gets confused if it encounters repeated -numbers, gaps, or lines that don't begin with a number.@refill - -@example -@{ - if ($1 > max) - max = $1 - arr[$1] = $0 -@} - -END @{ - for (x = 1; x <= max; x++) - print arr[x] -@} -@end example - -The first rule keeps track of the largest line number seen so far; -it also stores each line into the array @code{arr}, at an index that -is the line's number. - -The second rule runs after all the input has been read, to print out -all the lines. - -When this program is run with the following input: - -@example -5 I am the Five man -2 Who are you? The new number two! -4 . . . And four on the floor -1 Who is number one? -3 I three you. -@end example - -@noindent -its output is this: - -@example -1 Who is number one? -2 Who are you? The new number two! -3 I three you. -4 . . . And four on the floor -5 I am the Five man -@end example - -If a line number is repeated, the last line with a given number overrides -the others. - -Gaps in the line numbers can be handled with an easy improvement to the -program's @code{END} rule: - -@example -END @{ - for (x = 1; x <= max; x++) - if (x in arr) - print arr[x] -@} -@end example - -@node Scanning an Array, Delete, Array Example, Arrays -@section Scanning all Elements of an Array -@cindex @code{for (x in @dots{})} -@cindex arrays, special @code{for} statement -@cindex scanning an array - -In programs that use arrays, often you need a loop that executes -once for each element of an array. In other languages, where arrays are -contiguous and indices are limited to positive integers, this is -easy: the largest index is one less than the length of the array, and you can -find all the valid indices by counting from zero up to that value. This -technique won't do the job in @code{awk}, since any number or string -may be an array index. So @code{awk} has a special kind of @code{for} -statement for scanning an array: - -@example -for (@var{var} in @var{array}) - @var{body} -@end example - -@noindent -This loop executes @var{body} once for each different value that your -program has previously used as an index in @var{array}, with the -variable @var{var} set to that index.@refill - -Here is a program that uses this form of the @code{for} statement. The -first rule scans the input records and notes which words appear (at -least once) in the input, by storing a 1 into the array @code{used} with -the word as index. The second rule scans the elements of @code{used} to -find all the distinct words that appear in the input. It prints each -word that is more than 10 characters long, and also prints the number of -such words. @xref{Built-in, ,Built-in Functions}, for more information -on the built-in function @code{length}. - -@smallexample -# Record a 1 for each word that is used at least once. -@{ - for (i = 1; i <= NF; i++) - used[$i] = 1 -@} - -# Find number of distinct words more than 10 characters long. -END @{ - for (x in used) - if (length(x) > 10) @{ - ++num_long_words - print x - @} - print num_long_words, "words longer than 10 characters" -@} -@end smallexample - -@noindent -@xref{Sample Program}, for a more detailed example of this type. - -The order in which elements of the array are accessed by this statement -is determined by the internal arrangement of the array elements within -@code{awk} and cannot be controlled or changed. This can lead to -problems if new elements are added to @var{array} by statements in -@var{body}; you cannot predict whether or not the @code{for} loop will -reach them. Similarly, changing @var{var} inside the loop can produce -strange results. It is best to avoid such things.@refill - -@node Delete, Numeric Array Subscripts, Scanning an Array, Arrays -@section The @code{delete} Statement -@cindex @code{delete} statement -@cindex deleting elements of arrays -@cindex removing elements of arrays -@cindex arrays, deleting an element - -You can remove an individual element of an array using the @code{delete} -statement: - -@example -delete @var{array}[@var{index}] -@end example - -You can not refer to an array element after it has been deleted; -it is as if you had never referred -to it and had never given it any value. You can no longer obtain any -value the element once had. - -Here is an example of deleting elements in an array: - -@example -for (i in frequencies) - delete frequencies[i] -@end example - -@noindent -This example removes all the elements from the array @code{frequencies}. - -If you delete an element, a subsequent @code{for} statement to scan the array -will not report that element, and the @code{in} operator to check for -the presence of that element will return 0: - -@example -delete foo[4] -if (4 in foo) - print "This will never be printed" -@end example - -It is not an error to delete an element which does not exist. - -@node Numeric Array Subscripts, Multi-dimensional, Delete, Arrays -@section Using Numbers to Subscript Arrays - -An important aspect of arrays to remember is that array subscripts -are @emph{always} strings. If you use a numeric value as a subscript, -it will be converted to a string value before it is used for subscripting -(@pxref{Conversion, ,Conversion of Strings and Numbers}). - -@cindex conversions, during subscripting -@cindex numbers, used as subscripts -@vindex CONVFMT -This means that the value of the @code{CONVFMT} can potentially -affect how your program accesses elements of an array. For example: - -@example -a = b = 12.153 -data[a] = 1 -CONVFMT = "%2.2f" -if (b in data) - printf "%s is in data", b -else - printf "%s is not in data", b -@end example - -@noindent -should print @samp{12.15 is not in data}. The first statement gives -both @code{a} and @code{b} the same numeric value. Assigning to -@code{data[a]} first gives @code{a} the string value @code{"12.153"} -(using the default conversion value of @code{CONVFMT}, @code{"%.6g"}), -and then assigns 1 to @code{data["12.153"]}. The program then changes -the value of @code{CONVFMT}. The test @samp{(b in data)} forces @code{b} -to be converted to a string, this time @code{"12.15"}, since the value of -@code{CONVFMT} only allows two significant digits. This test fails, -since @code{"12.15"} is a different string from @code{"12.153"}.@refill - -According to the rules for conversions -(@pxref{Conversion, ,Conversion of Strings and Numbers}), integer -values are always converted to strings as integers, no matter what the -value of @code{CONVFMT} may happen to be. So the usual case of@refill - -@example -for (i = 1; i <= maxsub; i++) - @i{do something with} array[i] -@end example - -@noindent -will work, no matter what the value of @code{CONVFMT}. - -Like many things in @code{awk}, the majority of the time things work -as you would expect them to work. But it is useful to have a precise -knowledge of the actual rules, since sometimes they can have a subtle -effect on your programs. - -@node Multi-dimensional, Multi-scanning, Numeric Array Subscripts, Arrays -@section Multi-dimensional Arrays - -@c the following index entry is an overfull hbox. --mew 30jan1992 -@cindex subscripts in arrays -@cindex arrays, multi-dimensional subscripts -@cindex multi-dimensional subscripts -A multi-dimensional array is an array in which an element is identified -by a sequence of indices, not a single index. For example, a -two-dimensional array requires two indices. The usual way (in most -languages, including @code{awk}) to refer to an element of a -two-dimensional array named @code{grid} is with -@code{grid[@var{x},@var{y}]}. - -@vindex SUBSEP -Multi-dimensional arrays are supported in @code{awk} through -concatenation of indices into one string. What happens is that -@code{awk} converts the indices into strings -(@pxref{Conversion, ,Conversion of Strings and Numbers}) and -concatenates them together, with a separator between them. This creates -a single string that describes the values of the separate indices. The -combined string is used as a single index into an ordinary, -one-dimensional array. The separator used is the value of the built-in -variable @code{SUBSEP}.@refill - -For example, suppose we evaluate the expression @code{foo[5,12]="value"} -when the value of @code{SUBSEP} is @code{"@@"}. The numbers 5 and 12 are -converted to strings and -concatenated with an @samp{@@} between them, yielding @code{"5@@12"}; thus, -the array element @code{foo["5@@12"]} is set to @code{"value"}.@refill - -Once the element's value is stored, @code{awk} has no record of whether -it was stored with a single index or a sequence of indices. The two -expressions @code{foo[5,12]} and @w{@code{foo[5 SUBSEP 12]}} always have -the same value. - -The default value of @code{SUBSEP} is the string @code{"\034"}, -which contains a nonprinting character that is unlikely to appear in an -@code{awk} program or in the input data. - -The usefulness of choosing an unlikely character comes from the fact -that index values that contain a string matching @code{SUBSEP} lead to -combined strings that are ambiguous. Suppose that @code{SUBSEP} were -@code{"@@"}; then @w{@code{foo["a@@b", "c"]}} and @w{@code{foo["a", -"b@@c"]}} would be indistinguishable because both would actually be -stored as @code{foo["a@@b@@c"]}. Because @code{SUBSEP} is -@code{"\034"}, such confusion can arise only when an index -contains the character with ASCII code 034, which is a rare -event.@refill - -You can test whether a particular index-sequence exists in a -``multi-dimensional'' array with the same operator @code{in} used for single -dimensional arrays. Instead of a single index as the left-hand operand, -write the whole sequence of indices, separated by commas, in -parentheses:@refill - -@example -(@var{subscript1}, @var{subscript2}, @dots{}) in @var{array} -@end example - -The following example treats its input as a two-dimensional array of -fields; it rotates this array 90 degrees clockwise and prints the -result. It assumes that all lines have the same number of -elements. - -@example -awk '@{ - if (max_nf < NF) - max_nf = NF - max_nr = NR - for (x = 1; x <= NF; x++) - vector[x, NR] = $x -@} - -END @{ - for (x = 1; x <= max_nf; x++) @{ - for (y = max_nr; y >= 1; --y) - printf("%s ", vector[x, y]) - printf("\n") - @} -@}' -@end example - -@noindent -When given the input: - -@example -@group -1 2 3 4 5 6 -2 3 4 5 6 1 -3 4 5 6 1 2 -4 5 6 1 2 3 -@end group -@end example - -@noindent -it produces: - -@example -@group -4 3 2 1 -5 4 3 2 -6 5 4 3 -1 6 5 4 -2 1 6 5 -3 2 1 6 -@end group -@end example - -@node Multi-scanning, , Multi-dimensional, Arrays -@section Scanning Multi-dimensional Arrays - -There is no special @code{for} statement for scanning a -``multi-dimensional'' array; there cannot be one, because in truth there -are no multi-dimensional arrays or elements; there is only a -multi-dimensional @emph{way of accessing} an array. - -However, if your program has an array that is always accessed as -multi-dimensional, you can get the effect of scanning it by combining -the scanning @code{for} statement -(@pxref{Scanning an Array, ,Scanning all Elements of an Array}) with the -@code{split} built-in function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). -It works like this:@refill - -@example -for (combined in @var{array}) @{ - split(combined, separate, SUBSEP) - @dots{} -@} -@end example - -@noindent -This finds each concatenated, combined index in the array, and splits it -into the individual indices by breaking it apart where the value of -@code{SUBSEP} appears. The split-out indices become the elements of -the array @code{separate}. - -Thus, suppose you have previously stored in @code{@var{array}[1, -"foo"]}; then an element with index @code{"1\034foo"} exists in -@var{array}. (Recall that the default value of @code{SUBSEP} contains -the character with code 034.) Sooner or later the @code{for} statement -will find that index and do an iteration with @code{combined} set to -@code{"1\034foo"}. Then the @code{split} function is called as -follows: - -@example -split("1\034foo", separate, "\034") -@end example - -@noindent -The result of this is to set @code{separate[1]} to 1 and @code{separate[2]} -to @code{"foo"}. Presto, the original sequence of separate indices has -been recovered. - -@node Built-in, User-defined, Arrays, Top -@chapter Built-in Functions - -@cindex built-in functions -@dfn{Built-in} functions are functions that are always available for -your @code{awk} program to call. This chapter defines all the built-in -functions in @code{awk}; some of them are mentioned in other sections, -but they are summarized here for your convenience. (You can also define -new functions yourself. @xref{User-defined, ,User-defined Functions}.) - -@menu -* Calling Built-in:: How to call built-in functions. -* Numeric Functions:: Functions that work with numbers, - including @code{int}, @code{sin} and @code{rand}. -* String Functions:: Functions for string manipulation, - such as @code{split}, @code{match}, and @code{sprintf}. -* I/O Functions:: Functions for files and shell commands. -* Time Functions:: Functions for dealing with time stamps. -@end menu - -@node Calling Built-in, Numeric Functions, Built-in, Built-in -@section Calling Built-in Functions - -To call a built-in function, write the name of the function followed -by arguments in parentheses. For example, @code{atan2(y + z, 1)} -is a call to the function @code{atan2}, with two arguments. - -Whitespace is ignored between the built-in function name and the -open-parenthesis, but we recommend that you avoid using whitespace -there. User-defined functions do not permit whitespace in this way, and -you will find it easier to avoid mistakes by following a simple -convention which always works: no whitespace after a function name. - -Each built-in function accepts a certain number of arguments. In most -cases, any extra arguments given to built-in functions are ignored. The -defaults for omitted arguments vary from function to function and are -described under the individual functions. - -When a function is called, expressions that create the function's actual -parameters are evaluated completely before the function call is performed. -For example, in the code fragment: - -@example -i = 4 -j = sqrt(i++) -@end example - -@noindent -the variable @code{i} is set to 5 before @code{sqrt} is called -with a value of 4 for its actual parameter. - -@node Numeric Functions, String Functions, Calling Built-in, Built-in -@section Numeric Built-in Functions -@c I didn't make all the examples small because a couple of them were -@c short already. --mew 29jan1992 - -Here is a full list of built-in functions that work with numbers: - -@table @code -@item int(@var{x}) -This gives you the integer part of @var{x}, truncated toward 0. This -produces the nearest integer to @var{x}, located between @var{x} and 0. - -For example, @code{int(3)} is 3, @code{int(3.9)} is 3, @code{int(-3.9)} -is @minus{}3, and @code{int(-3)} is @minus{}3 as well.@refill - -@item sqrt(@var{x}) -This gives you the positive square root of @var{x}. It reports an error -if @var{x} is negative. Thus, @code{sqrt(4)} is 2.@refill - -@item exp(@var{x}) -This gives you the exponential of @var{x}, or reports an error if -@var{x} is out of range. The range of values @var{x} can have depends -on your machine's floating point representation.@refill - -@item log(@var{x}) -This gives you the natural logarithm of @var{x}, if @var{x} is positive; -otherwise, it reports an error.@refill - -@item sin(@var{x}) -This gives you the sine of @var{x}, with @var{x} in radians. - -@item cos(@var{x}) -This gives you the cosine of @var{x}, with @var{x} in radians. - -@item atan2(@var{y}, @var{x}) -This gives you the arctangent of @code{@var{y} / @var{x}} in radians. - -@item rand() -This gives you a random number. The values of @code{rand} are -uniformly-distributed between 0 and 1. The value is never 0 and never -1. - -Often you want random integers instead. Here is a user-defined function -you can use to obtain a random nonnegative integer less than @var{n}: - -@example -function randint(n) @{ - return int(n * rand()) -@} -@end example - -@noindent -The multiplication produces a random real number greater than 0 and less -than @var{n}. We then make it an integer (using @code{int}) between 0 -and @code{@var{n} @minus{} 1}. - -Here is an example where a similar function is used to produce -random integers between 1 and @var{n}. Note that this program will -print a new random number for each input record. - -@smallexample -awk ' -# Function to roll a simulated die. -function roll(n) @{ return 1 + int(rand() * n) @} - -# Roll 3 six-sided dice and print total number of points. -@{ - printf("%d points\n", roll(6)+roll(6)+roll(6)) -@}' -@end smallexample - -@strong{Note:} @code{rand} starts generating numbers from the same -point, or @dfn{seed}, each time you run @code{awk}. This means that -a program will produce the same results each time you run it. -The numbers are random within one @code{awk} run, but predictable -from run to run. This is convenient for debugging, but if you want -a program to do different things each time it is used, you must change -the seed to a value that will be different in each run. To do this, -use @code{srand}. - -@item srand(@var{x}) -The function @code{srand} sets the starting point, or @dfn{seed}, -for generating random numbers to the value @var{x}. - -Each seed value leads to a particular sequence of ``random'' numbers. -Thus, if you set the seed to the same value a second time, you will get -the same sequence of ``random'' numbers again. - -If you omit the argument @var{x}, as in @code{srand()}, then the current -date and time of day are used for a seed. This is the way to get random -numbers that are truly unpredictable. - -The return value of @code{srand} is the previous seed. This makes it -easy to keep track of the seeds for use in consistently reproducing -sequences of random numbers. -@end table - -@node String Functions, I/O Functions, Numeric Functions, Built-in -@section Built-in Functions for String Manipulation - -The functions in this section look at or change the text of one or more -strings. - -@table @code -@item index(@var{in}, @var{find}) -@findex match -This searches the string @var{in} for the first occurrence of the string -@var{find}, and returns the position in characters where that occurrence -begins in the string @var{in}. For example:@refill - -@smallexample -awk 'BEGIN @{ print index("peanut", "an") @}' -@end smallexample - -@noindent -prints @samp{3}. If @var{find} is not found, @code{index} returns 0. -(Remember that string indices in @code{awk} start at 1.) - -@item length(@var{string}) -@findex length -This gives you the number of characters in @var{string}. If -@var{string} is a number, the length of the digit string representing -that number is returned. For example, @code{length("abcde")} is 5. By -contrast, @code{length(15 * 35)} works out to 3. How? Well, 15 * 35 = -525, and 525 is then converted to the string @samp{"525"}, which has -three characters. - -If no argument is supplied, @code{length} returns the length of @code{$0}. - -In older versions of @code{awk}, you could call the @code{length} function -without any parentheses. Doing so is marked as ``deprecated'' in the -@sc{posix} standard. This means that while you can do this in your -programs, it is a feature that can eventually be removed from a future -version of the standard. Therefore, for maximal portability of your -@code{awk} programs you should always supply the parentheses. - -@item match(@var{string}, @var{regexp}) -@findex match -The @code{match} function searches the string, @var{string}, for the -longest, leftmost substring matched by the regular expression, -@var{regexp}. It returns the character position, or @dfn{index}, of -where that substring begins (1, if it starts at the beginning of -@var{string}). If no match if found, it returns 0. - -@vindex RSTART -@vindex RLENGTH -The @code{match} function sets the built-in variable @code{RSTART} to -the index. It also sets the built-in variable @code{RLENGTH} to the -length in characters of the matched substring. If no match is found, -@code{RSTART} is set to 0, and @code{RLENGTH} to @minus{}1. - -For example: - -@smallexample -awk '@{ - if ($1 == "FIND") - regex = $2 - else @{ - where = match($0, regex) - if (where) - print "Match of", regex, "found at", where, "in", $0 - @} -@}' -@end smallexample - -@noindent -This program looks for lines that match the regular expression stored in -the variable @code{regex}. This regular expression can be changed. If the -first word on a line is @samp{FIND}, @code{regex} is changed to be the -second word on that line. Therefore, given: - -@smallexample -FIND fo*bar -My program was a foobar -But none of it would doobar -FIND Melvin -JF+KM -This line is property of The Reality Engineering Co. -This file created by Melvin. -@end smallexample - -@noindent -@code{awk} prints: - -@smallexample -Match of fo*bar found at 18 in My program was a foobar -Match of Melvin found at 26 in This file created by Melvin. -@end smallexample - -@item split(@var{string}, @var{array}, @var{fieldsep}) -@findex split -This divides @var{string} into pieces separated by @var{fieldsep}, -and stores the pieces in @var{array}. The first piece is stored in -@code{@var{array}[1]}, the second piece in @code{@var{array}[2]}, and so -forth. The string value of the third argument, @var{fieldsep}, is -a regexp describing where to split @var{string} (much as @code{FS} can -be a regexp describing where to split input records). If -the @var{fieldsep} is omitted, the value of @code{FS} is used. -@code{split} returns the number of elements created.@refill - -The @code{split} function, then, splits strings into pieces in a -manner similar to the way input lines are split into fields. For example: - -@smallexample -split("auto-da-fe", a, "-") -@end smallexample - -@noindent -splits the string @samp{auto-da-fe} into three fields using @samp{-} as the -separator. It sets the contents of the array @code{a} as follows: - -@smallexample -a[1] = "auto" -a[2] = "da" -a[3] = "fe" -@end smallexample - -@noindent -The value returned by this call to @code{split} is 3. - -As with input field-splitting, when the value of @var{fieldsep} is -@code{" "}, leading and trailing whitespace is ignored, and the elements -are separated by runs of whitespace. - -@item sprintf(@var{format}, @var{expression1},@dots{}) -@findex sprintf -This returns (without printing) the string that @code{printf} would -have printed out with the same arguments -(@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}). -For example:@refill - -@smallexample -sprintf("pi = %.2f (approx.)", 22/7) -@end smallexample - -@noindent -returns the string @w{@code{"pi = 3.14 (approx.)"}}. - -@item sub(@var{regexp}, @var{replacement}, @var{target}) -@findex sub -The @code{sub} function alters the value of @var{target}. -It searches this value, which should be a string, for the -leftmost substring matched by the regular expression, @var{regexp}, -extending this match as far as possible. Then the entire string is -changed by replacing the matched text with @var{replacement}. -The modified string becomes the new value of @var{target}. - -This function is peculiar because @var{target} is not simply -used to compute a value, and not just any expression will do: it -must be a variable, field or array reference, so that @code{sub} can -store a modified value there. If this argument is omitted, then the -default is to use and alter @code{$0}. - -For example:@refill - -@smallexample -str = "water, water, everywhere" -sub(/at/, "ith", str) -@end smallexample - -@noindent -sets @code{str} to @w{@code{"wither, water, everywhere"}}, by replacing the -leftmost, longest occurrence of @samp{at} with @samp{ith}. - -The @code{sub} function returns the number of substitutions made (either -one or zero). - -If the special character @samp{&} appears in @var{replacement}, it -stands for the precise substring that was matched by @var{regexp}. (If -the regexp can match more than one string, then this precise substring -may vary.) For example:@refill - -@smallexample -awk '@{ sub(/candidate/, "& and his wife"); print @}' -@end smallexample - -@noindent -changes the first occurrence of @samp{candidate} to @samp{candidate -and his wife} on each input line. - -Here is another example: - -@smallexample -awk 'BEGIN @{ - str = "daabaaa" - sub(/a*/, "c&c", str) - print str -@}' -@end smallexample - -@noindent -prints @samp{dcaacbaaa}. This show how @samp{&} can represent a non-constant -string, and also illustrates the ``leftmost, longest'' rule. - -The effect of this special character (@samp{&}) can be turned off by putting a -backslash before it in the string. As usual, to insert one backslash in -the string, you must write two backslashes. Therefore, write @samp{\\&} -in a string constant to include a literal @samp{&} in the replacement. -For example, here is how to replace the first @samp{|} on each line with -an @samp{&}:@refill - -@smallexample -awk '@{ sub(/\|/, "\\&"); print @}' -@end smallexample - -@strong{Note:} as mentioned above, the third argument to @code{sub} must -be an lvalue. Some versions of @code{awk} allow the third argument to -be an expression which is not an lvalue. In such a case, @code{sub} -would still search for the pattern and return 0 or 1, but the result of -the substitution (if any) would be thrown away because there is no place -to put it. Such versions of @code{awk} accept expressions like -this:@refill - -@smallexample -sub(/USA/, "United States", "the USA and Canada") -@end smallexample - -@noindent -But that is considered erroneous in @code{gawk}. - -@item gsub(@var{regexp}, @var{replacement}, @var{target}) -@findex gsub -This is similar to the @code{sub} function, except @code{gsub} replaces -@emph{all} of the longest, leftmost, @emph{nonoverlapping} matching -substrings it can find. The @samp{g} in @code{gsub} stands for -``global,'' which means replace everywhere. For example:@refill - -@smallexample -awk '@{ gsub(/Britain/, "United Kingdom"); print @}' -@end smallexample - -@noindent -replaces all occurrences of the string @samp{Britain} with @samp{United -Kingdom} for all input records.@refill - -The @code{gsub} function returns the number of substitutions made. If -the variable to be searched and altered, @var{target}, is -omitted, then the entire input record, @code{$0}, is used.@refill - -As in @code{sub}, the characters @samp{&} and @samp{\} are special, and -the third argument must be an lvalue. - -@item substr(@var{string}, @var{start}, @var{length}) -@findex substr -This returns a @var{length}-character-long substring of @var{string}, -starting at character number @var{start}. The first character of a -string is character number one. For example, -@code{substr("washington", 5, 3)} returns @code{"ing"}.@refill - -If @var{length} is not present, this function returns the whole suffix of -@var{string} that begins at character number @var{start}. For example, -@code{substr("washington", 5)} returns @code{"ington"}. This is also -the case if @var{length} is greater than the number of characters remaining -in the string, counting from character number @var{start}. - -@item tolower(@var{string}) -@findex tolower -This returns a copy of @var{string}, with each upper-case character -in the string replaced with its corresponding lower-case character. -Nonalphabetic characters are left unchanged. For example, -@code{tolower("MiXeD cAsE 123")} returns @code{"mixed case 123"}. - -@item toupper(@var{string}) -@findex toupper -This returns a copy of @var{string}, with each lower-case character -in the string replaced with its corresponding upper-case character. -Nonalphabetic characters are left unchanged. For example, -@code{toupper("MiXeD cAsE 123")} returns @code{"MIXED CASE 123"}. -@end table - -@node I/O Functions, Time Functions, String Functions, Built-in -@section Built-in Functions for Input/Output - -@table @code -@item close(@var{filename}) -Close the file @var{filename}, for input or output. The argument may -alternatively be a shell command that was used for redirecting to or -from a pipe; then the pipe is closed. - -@xref{Close Input, ,Closing Input Files and Pipes}, regarding closing -input files and pipes. @xref{Close Output, ,Closing Output Files and Pipes}, -regarding closing output files and pipes.@refill - -@item system(@var{command}) -@findex system -@c the following index entry is an overfull hbox. --mew 30jan1992 -@cindex interaction, @code{awk} and other programs -The system function allows the user to execute operating system commands -and then return to the @code{awk} program. The @code{system} function -executes the command given by the string @var{command}. It returns, as -its value, the status returned by the command that was executed. - -For example, if the following fragment of code is put in your @code{awk} -program: - -@smallexample -END @{ - system("mail -s 'awk run done' operator < /dev/null") -@} -@end smallexample - -@noindent -the system operator will be sent mail when the @code{awk} program -finishes processing input and begins its end-of-input processing. - -Note that much the same result can be obtained by redirecting -@code{print} or @code{printf} into a pipe. However, if your @code{awk} -program is interactive, @code{system} is useful for cranking up large -self-contained programs, such as a shell or an editor.@refill - -Some operating systems cannot implement the @code{system} function. -@code{system} causes a fatal error if it is not supported. -@end table - -@c fakenode --- for prepinfo -@subheading Controlling Output Buffering with @code{system} -@cindex flushing buffers -@cindex buffers, flushing -@cindex buffering output -@cindex output, buffering - -Many utility programs will @dfn{buffer} their output; they save information -to be written to a disk file or terminal in memory, until there is enough -to be written in one operation. This is often more efficient than writing -every little bit of information as soon as it is ready. However, sometimes -it is necessary to force a program to @dfn{flush} its buffers; that is, -write the information to its destination, even if a buffer is not full. -You can do this from your @code{awk} program by calling @code{system} -with a null string as its argument: - -@example -system("") # flush output -@end example - -@noindent -@code{gawk} treats this use of the @code{system} function as a special -case, and is smart enough not to run a shell (or other command -interpreter) with the empty command. Therefore, with @code{gawk}, this -idiom is not only useful, it is efficient. While this idiom should work -with other @code{awk} implementations, it will not necessarily avoid -starting an unnecessary shell. -@ignore -Need a better explanation, perhaps in a separate paragraph. Explain that -for - -awk 'BEGIN { print "hi" - system("echo hello") - print "howdy" }' - -that the output had better be - - hi - hello - howdy - -and not - - hello - hi - howdy - -which it would be if awk did not flush its buffers before calling system. -@end ignore - -@node Time Functions, , I/O Functions, Built-in -@section Functions for Dealing with Time Stamps - -@cindex time stamps -@cindex time of day -A common use for @code{awk} programs is the processing of log files. -Log files often contain time stamp information, indicating when a -particular log record was written. Many programs log their time stamp -in the form returned by the @code{time} system call, which is the -number of seconds since a particular epoch. On @sc{posix} systems, -it is the number of seconds since Midnight, January 1, 1970, @sc{utc}. - -In order to make it easier to process such log files, and to easily produce -useful reports, @code{gawk} provides two functions for working with time -stamps. Both of these are @code{gawk} extensions; they are not specified -in the @sc{posix} standard, nor are they in any other known version -of @code{awk}. - -@table @code -@item systime() -@findex systime -This function returns the current time as the number of seconds since -the system epoch. On @sc{posix} systems, this is the number of seconds -since Midnight, January 1, 1970, @sc{utc}. It may be a different number on -other systems. - -@item strftime(@var{format}, @var{timestamp}) -@findex strftime -This function returns a string. It is similar to the function of the -same name in the @sc{ansi} C standard library. The time specified by -@var{timestamp} is used to produce a string, based on the contents -of the @var{format} string. -@end table - -The @code{systime} function allows you to compare a time stamp from a -log file with the current time of day. In particular, it is easy to -determine how long ago a particular record was logged. It also allows -you to produce log records using the ``seconds since the epoch'' format. - -The @code{strftime} function allows you to easily turn a time stamp -into human-readable information. It is similar in nature to the @code{sprintf} -function, copying non-format specification characters verbatim to the -returned string, and substituting date and time values for format -specifications in the @var{format} string. If no @var{timestamp} argument -is supplied, @code{gawk} will use the current time of day as the -time stamp.@refill - -@code{strftime} is guaranteed by the @sc{ansi} C standard to support -the following date format specifications: - -@table @code -@item %a -The locale's abbreviated weekday name. - -@item %A -The locale's full weekday name. - -@item %b -The locale's abbreviated month name. - -@item %B -The locale's full month name. - -@item %c -The locale's ``appropriate'' date and time representation. - -@item %d -The day of the month as a decimal number (01--31). - -@item %H -The hour (24-hour clock) as a decimal number (00--23). - -@item %I -The hour (12-hour clock) as a decimal number (01--12). - -@item %j -The day of the year as a decimal number (001--366). - -@item %m -The month as a decimal number (01--12). - -@item %M -The minute as a decimal number (00--59). - -@item %p -The locale's equivalent of the AM/PM designations associated -with a 12-hour clock. - -@item %S -The second as a decimal number (00--61). (Occasionally there are -minutes in a year with one or two leap seconds, which is why the -seconds can go from 0 all the way to 61.) - -@item %U -The week number of the year (the first Sunday as the first day of week 1) -as a decimal number (00--53). - -@item %w -The weekday as a decimal number (0--6). Sunday is day 0. - -@item %W -The week number of the year (the first Monday as the first day of week 1) -as a decimal number (00--53). - -@item %x -The locale's ``appropriate'' date representation. - -@item %X -The locale's ``appropriate'' time representation. - -@item %y -The year without century as a decimal number (00--99). - -@item %Y -The year with century as a decimal number. - -@item %Z -The time zone name or abbreviation, or no characters if -no time zone is determinable. - -@item %% -A literal @samp{%}. -@end table - -@c The parenthetical remark here should really be a footnote, but -@c it gave formatting problems at the FSF. So for now put it in -@c parentheses. -If a conversion specifier is not one of the above, the behavior is -undefined. (This is because the @sc{ansi} standard for C leaves the -behavior of the C version of @code{strftime} undefined, and @code{gawk} -will use the system's version of @code{strftime} if it's there. -Typically, the conversion specifier will either not appear in the -returned string, or it will appear literally.) - -Informally, a @dfn{locale} is the geographic place in which a program -is meant to run. For example, a common way to abbreviate the date -September 4, 1991 in the United States would be ``9/4/91''. -In many countries in Europe, however, it would be abbreviated ``4.9.91''. -Thus, the @samp{%x} specification in a @code{"US"} locale might produce -@samp{9/4/91}, while in a @code{"EUROPE"} locale, it might produce -@samp{4.9.91}. The @sc{ansi} C standard defines a default @code{"C"} -locale, which is an environment that is typical of what most C programmers -are used to. - -A public-domain C version of @code{strftime} is shipped with @code{gawk} -for systems that are not yet fully @sc{ansi}-compliant. If that version is -used to compile @code{gawk} (@pxref{Installation, ,Installing @code{gawk}}), -then the following additional format specifications are available:@refill - -@table @code -@item %D -Equivalent to specifying @samp{%m/%d/%y}. - -@item %e -The day of the month, padded with a blank if it is only one digit. - -@item %h -Equivalent to @samp{%b}, above. - -@item %n -A newline character (ASCII LF). - -@item %r -Equivalent to specifying @samp{%I:%M:%S %p}. - -@item %R -Equivalent to specifying @samp{%H:%M}. - -@item %T -Equivalent to specifying @samp{%H:%M:%S}. - -@item %t -A TAB character. - -@item %k -is replaced by the hour (24-hour clock) as a decimal number (0-23). -Single digit numbers are padded with a blank. - -@item %l -is replaced by the hour (12-hour clock) as a decimal number (1-12). -Single digit numbers are padded with a blank. - -@item %C -The century, as a number between 00 and 99. - -@item %u -is replaced by the weekday as a decimal number -[1 (Monday)--7]. - -@item %V -is replaced by the week number of the year (the first Monday as the first -day of week 1) as a decimal number (01--53). -The method for determining the week number is as specified by ISO 8601 -(to wit: if the week containing January 1 has four or more days in the -new year, then it is week 1, otherwise it is week 53 of the previous year -and the next week is week 1).@refill - -@item %Ec %EC %Ex %Ey %EY %Od %Oe %OH %OI -@itemx %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy -These are ``alternate representations'' for the specifications -that use only the second letter (@samp{%c}, @samp{%C}, and so on). -They are recognized, but their normal representations are used. -(These facilitate compliance with the @sc{posix} @code{date} -utility.)@refill - -@item %v -The date in VMS format (e.g. 20-JUN-1991). -@end table - -Here are two examples that use @code{strftime}. The first is an -@code{awk} version of the C @code{ctime} function. (This is a -user defined function, which we have not discussed yet. -@xref{User-defined, ,User-defined Functions}, for more information.) - -@smallexample -# ctime.awk -# -# awk version of C ctime(3) function - -function ctime(ts, format) -@{ - format = "%a %b %e %H:%M:%S %Z %Y" - if (ts == 0) - ts = systime() # use current time as default - return strftime(format, ts) -@} -@end smallexample - -This next example is an @code{awk} implementation of the @sc{posix} -@code{date} utility. Normally, the @code{date} utility prints the -current date and time of day in a well known format. However, if you -provide an argument to it that begins with a @samp{+}, @code{date} -will copy non-format specifier characters to the standard output, and -will interpret the current time according to the format specifiers in -the string. For example: - -@smallexample -date '+Today is %A, %B %d, %Y.' -@end smallexample - -@noindent -might print - -@smallexample -Today is Thursday, July 11, 1991. -@end smallexample - -Here is the @code{awk} version of the @code{date} utility. - -@smallexample -#! /usr/bin/gawk -f -# -# date --- implement the P1003.2 Draft 11 'date' command -# -# Bug: does not recognize the -u argument. - -BEGIN \ -@{ - format = "%a %b %e %H:%M:%S %Z %Y" - exitval = 0 - - if (ARGC > 2) - exitval = 1 - else if (ARGC == 2) @{ - format = ARGV[1] - if (format ~ /^\+/) - format = substr(format, 2) # remove leading + - @} - print strftime(format) - exit exitval -@} -@end smallexample - -@node User-defined, Built-in Variables, Built-in, Top -@chapter User-defined Functions - -@cindex user-defined functions -@cindex functions, user-defined -Complicated @code{awk} programs can often be simplified by defining -your own functions. User-defined functions can be called just like -built-in ones (@pxref{Function Calls}), but it is up to you to define -them---to tell @code{awk} what they should do. - -@menu -* Definition Syntax:: How to write definitions and what they mean. -* Function Example:: An example function definition and - what it does. -* Function Caveats:: Things to watch out for. -* Return Statement:: Specifying the value a function returns. -@end menu - -@node Definition Syntax, Function Example, User-defined, User-defined -@section Syntax of Function Definitions -@cindex defining functions -@cindex function definition - -Definitions of functions can appear anywhere between the rules of the -@code{awk} program. Thus, the general form of an @code{awk} program is -extended to include sequences of rules @emph{and} user-defined function -definitions. - -The definition of a function named @var{name} looks like this: - -@example -function @var{name} (@var{parameter-list}) @{ - @var{body-of-function} -@} -@end example - -@noindent -@var{name} is the name of the function to be defined. A valid function -name is like a valid variable name: a sequence of letters, digits and -underscores, not starting with a digit. Functions share the same pool -of names as variables and arrays. - -@var{parameter-list} is a list of the function's arguments and local -variable names, separated by commas. When the function is called, -the argument names are used to hold the argument values given in -the call. The local variables are initialized to the null string. - -The @var{body-of-function} consists of @code{awk} statements. It is the -most important part of the definition, because it says what the function -should actually @emph{do}. The argument names exist to give the body a -way to talk about the arguments; local variables, to give the body -places to keep temporary values. - -Argument names are not distinguished syntactically from local variable -names; instead, the number of arguments supplied when the function is -called determines how many argument variables there are. Thus, if three -argument values are given, the first three names in @var{parameter-list} -are arguments, and the rest are local variables. - -It follows that if the number of arguments is not the same in all calls -to the function, some of the names in @var{parameter-list} may be -arguments on some occasions and local variables on others. Another -way to think of this is that omitted arguments default to the -null string. - -Usually when you write a function you know how many names you intend to -use for arguments and how many you intend to use as locals. By -convention, you should write an extra space between the arguments and -the locals, so other people can follow how your function is -supposed to be used. - -During execution of the function body, the arguments and local variable -values hide or @dfn{shadow} any variables of the same names used in the -rest of the program. The shadowed variables are not accessible in the -function definition, because there is no way to name them while their -names have been taken away for the local variables. All other variables -used in the @code{awk} program can be referenced or set normally in the -function definition. - -The arguments and local variables last only as long as the function body -is executing. Once the body finishes, the shadowed variables come back. - -The function body can contain expressions which call functions. They -can even call this function, either directly or by way of another -function. When this happens, we say the function is @dfn{recursive}. - -There is no need in @code{awk} to put the definition of a function -before all uses of the function. This is because @code{awk} reads the -entire program before starting to execute any of it. - -In many @code{awk} implementations, the keyword @code{function} may be -abbreviated @code{func}. However, @sc{posix} only specifies the use of -the keyword @code{function}. This actually has some practical implications. -If @code{gawk} is in @sc{posix}-compatibility mode -(@pxref{Command Line, ,Invoking @code{awk}}), then the following -statement will @emph{not} define a function:@refill - -@example -func foo() @{ a = sqrt($1) ; print a @} -@end example - -@noindent -Instead it defines a rule that, for each record, concatenates the value -of the variable @samp{func} with the return value of the function @samp{foo}, -and based on the truth value of the result, executes the corresponding action. -This is probably not what was desired. (@code{awk} accepts this input as -syntactically valid, since functions may be used before they are defined -in @code{awk} programs.) - -@node Function Example, Function Caveats, Definition Syntax, User-defined -@section Function Definition Example - -Here is an example of a user-defined function, called @code{myprint}, that -takes a number and prints it in a specific format. - -@example -function myprint(num) -@{ - printf "%6.3g\n", num -@} -@end example - -@noindent -To illustrate, here is an @code{awk} rule which uses our @code{myprint} -function: - -@example -$3 > 0 @{ myprint($3) @} -@end example - -@noindent -This program prints, in our special format, all the third fields that -contain a positive number in our input. Therefore, when given: - -@example - 1.2 3.4 5.6 7.8 - 9.10 11.12 -13.14 15.16 -17.18 19.20 21.22 23.24 -@end example - -@noindent -this program, using our function to format the results, prints: - -@example - 5.6 - 21.2 -@end example - -Here is a rather contrived example of a recursive function. It prints a -string backwards: - -@example -function rev (str, len) @{ - if (len == 0) @{ - printf "\n" - return - @} - printf "%c", substr(str, len, 1) - rev(str, len - 1) -@} -@end example - -@node Function Caveats, Return Statement, Function Example, User-defined -@section Calling User-defined Functions - -@dfn{Calling a function} means causing the function to run and do its job. -A function call is an expression, and its value is the value returned by -the function. - -A function call consists of the function name followed by the arguments -in parentheses. What you write in the call for the arguments are -@code{awk} expressions; each time the call is executed, these -expressions are evaluated, and the values are the actual arguments. For -example, here is a call to @code{foo} with three arguments (the first -being a string concatenation): - -@example -foo(x y, "lose", 4 * z) -@end example - -@quotation -@strong{Caution:} whitespace characters (spaces and tabs) are not allowed -between the function name and the open-parenthesis of the argument list. -If you write whitespace by mistake, @code{awk} might think that you mean -to concatenate a variable with an expression in parentheses. However, it -notices that you used a function name and not a variable name, and reports -an error. -@end quotation - -@cindex call by value -When a function is called, it is given a @emph{copy} of the values of -its arguments. This is called @dfn{call by value}. The caller may use -a variable as the expression for the argument, but the called function -does not know this: it only knows what value the argument had. For -example, if you write this code: - -@example -foo = "bar" -z = myfunc(foo) -@end example - -@noindent -then you should not think of the argument to @code{myfunc} as being -``the variable @code{foo}.'' Instead, think of the argument as the -string value, @code{"bar"}. - -If the function @code{myfunc} alters the values of its local variables, -this has no effect on any other variables. In particular, if @code{myfunc} -does this: - -@example -function myfunc (win) @{ - print win - win = "zzz" - print win -@} -@end example - -@noindent -to change its first argument variable @code{win}, this @emph{does not} -change the value of @code{foo} in the caller. The role of @code{foo} in -calling @code{myfunc} ended when its value, @code{"bar"}, was computed. -If @code{win} also exists outside of @code{myfunc}, the function body -cannot alter this outer value, because it is shadowed during the -execution of @code{myfunc} and cannot be seen or changed from there. - -@cindex call by reference -However, when arrays are the parameters to functions, they are @emph{not} -copied. Instead, the array itself is made available for direct manipulation -by the function. This is usually called @dfn{call by reference}. -Changes made to an array parameter inside the body of a function @emph{are} -visible outside that function. -@ifinfo -This can be @strong{very} dangerous if you do not watch what you are -doing. For example:@refill -@end ifinfo -@iftex -@emph{This can be very dangerous if you do not watch what you are -doing.} For example:@refill -@end iftex - -@example -function changeit (array, ind, nvalue) @{ - array[ind] = nvalue -@} - -BEGIN @{ - a[1] = 1 ; a[2] = 2 ; a[3] = 3 - changeit(a, 2, "two") - printf "a[1] = %s, a[2] = %s, a[3] = %s\n", a[1], a[2], a[3] - @} -@end example - -@noindent -prints @samp{a[1] = 1, a[2] = two, a[3] = 3}, because calling -@code{changeit} stores @code{"two"} in the second element of @code{a}. - -@node Return Statement, , Function Caveats, User-defined -@section The @code{return} Statement -@cindex @code{return} statement - -The body of a user-defined function can contain a @code{return} statement. -This statement returns control to the rest of the @code{awk} program. It -can also be used to return a value for use in the rest of the @code{awk} -program. It looks like this:@refill - -@example -return @var{expression} -@end example - -The @var{expression} part is optional. If it is omitted, then the returned -value is undefined and, therefore, unpredictable. - -A @code{return} statement with no value expression is assumed at the end of -every function definition. So if control reaches the end of the function -body, then the function returns an unpredictable value. @code{awk} -will not warn you if you use the return value of such a function; you will -simply get unpredictable or unexpected results. - -Here is an example of a user-defined function that returns a value -for the largest number among the elements of an array:@refill - -@example -@group -function maxelt (vec, i, ret) @{ - for (i in vec) @{ - if (ret == "" || vec[i] > ret) - ret = vec[i] - @} - return ret -@} -@end group -@end example - -@noindent -You call @code{maxelt} with one argument, which is an array name. The local -variables @code{i} and @code{ret} are not intended to be arguments; -while there is nothing to stop you from passing two or three arguments -to @code{maxelt}, the results would be strange. The extra space before -@code{i} in the function parameter list is to indicate that @code{i} and -@code{ret} are not supposed to be arguments. This is a convention which -you should follow when you define functions. - -Here is a program that uses our @code{maxelt} function. It loads an -array, calls @code{maxelt}, and then reports the maximum number in that -array:@refill - -@example -@group -awk ' -function maxelt (vec, i, ret) @{ - for (i in vec) @{ - if (ret == "" || vec[i] > ret) - ret = vec[i] - @} - return ret -@} -@end group - -@group -# Load all fields of each record into nums. -@{ - for(i = 1; i <= NF; i++) - nums[NR, i] = $i -@} - -END @{ - print maxelt(nums) -@}' -@end group -@end example - -Given the following input: - -@example -@group - 1 5 23 8 16 -44 3 5 2 8 26 -256 291 1396 2962 100 --6 467 998 1101 -99385 11 0 225 -@end group -@end example - -@noindent -our program tells us (predictably) that: - -@example -99385 -@end example - -@noindent -is the largest number in our array. - -@node Built-in Variables, Command Line, User-defined, Top -@chapter Built-in Variables -@cindex built-in variables - -Most @code{awk} variables are available for you to use for your own -purposes; they never change except when your program assigns values to -them, and never affect anything except when your program examines them. - -A few variables have special built-in meanings. Some of them @code{awk} -examines automatically, so that they enable you to tell @code{awk} how -to do certain things. Others are set automatically by @code{awk}, so -that they carry information from the internal workings of @code{awk} to -your program. - -This chapter documents all the built-in variables of @code{gawk}. Most -of them are also documented in the chapters where their areas of -activity are described. - -@menu -* User-modified:: Built-in variables that you change - to control @code{awk}. -* Auto-set:: Built-in variables where @code{awk} - gives you information. -@end menu - -@node User-modified, Auto-set, Built-in Variables, Built-in Variables -@section Built-in Variables that Control @code{awk} -@cindex built-in variables, user modifiable - -This is a list of the variables which you can change to control how -@code{awk} does certain things. - -@table @code -@iftex -@vindex CONVFMT -@end iftex -@item CONVFMT -This string is used by @code{awk} to control conversion of numbers to -strings (@pxref{Conversion, ,Conversion of Strings and Numbers}). -It works by being passed, in effect, as the first argument to the -@code{sprintf} function. Its default value is @code{"%.6g"}. -@code{CONVFMT} was introduced by the @sc{posix} standard.@refill - -@iftex -@vindex FIELDWIDTHS -@end iftex -@item FIELDWIDTHS -This is a space separated list of columns that tells @code{gawk} -how to manage input with fixed, columnar boundaries. It is an -experimental feature that is still evolving. Assigning to @code{FIELDWIDTHS} -overrides the use of @code{FS} for field splitting. -@xref{Constant Size, ,Reading Fixed-width Data}, for more information.@refill - -If @code{gawk} is in compatibility mode -(@pxref{Command Line, ,Invoking @code{awk}}), then @code{FIELDWIDTHS} -has no special meaning, and field splitting operations are done based -exclusively on the value of @code{FS}.@refill - -@iftex -@vindex FS -@end iftex -@item FS -@code{FS} is the input field separator -(@pxref{Field Separators, ,Specifying how Fields are Separated}). -The value is a single-character string or a multi-character regular -expression that matches the separations between fields in an input -record.@refill - -The default value is @w{@code{" "}}, a string consisting of a single -space. As a special exception, this value actually means that any -sequence of spaces and tabs is a single separator. It also causes -spaces and tabs at the beginning or end of a line to be ignored. - -You can set the value of @code{FS} on the command line using the -@samp{-F} option: - -@example -awk -F, '@var{program}' @var{input-files} -@end example - -If @code{gawk} is using @code{FIELDWIDTHS} for field-splitting, -assigning a value to @code{FS} will cause @code{gawk} to return to -the normal, regexp-based, field splitting. - -@item IGNORECASE -@iftex -@vindex IGNORECASE -@end iftex -If @code{IGNORECASE} is nonzero, then @emph{all} regular expression -matching is done in a case-independent fashion. In particular, regexp -matching with @samp{~} and @samp{!~}, and the @code{gsub} @code{index}, -@code{match}, @code{split} and @code{sub} functions all ignore case when -doing their particular regexp operations. @strong{Note:} since field -splitting with the value of the @code{FS} variable is also a regular -expression operation, that too is done with case ignored. -@xref{Case-sensitivity, ,Case-sensitivity in Matching}. - -If @code{gawk} is in compatibility mode -(@pxref{Command Line, ,Invoking @code{awk}}), then @code{IGNORECASE} has -no special meaning, and regexp operations are always case-sensitive.@refill - -@item OFMT -@iftex -@vindex OFMT -@end iftex -This string is used by @code{awk} to control conversion of numbers to -strings (@pxref{Conversion, ,Conversion of Strings and Numbers}) for -printing with the @code{print} statement. -It works by being passed, in effect, as the first argument to the -@code{sprintf} function. Its default value is @code{"%.6g"}. -Earlier versions of @code{awk} also used @code{OFMT} to specify the -format for converting numbers to strings in general expressions; this -has been taken over by @code{CONVFMT}.@refill - -@item OFS -@iftex -@vindex OFS -@end iftex -This is the output field separator (@pxref{Output Separators}). It is -output between the fields output by a @code{print} statement. Its -default value is @w{@code{" "}}, a string consisting of a single space. - -@item ORS -@iftex -@vindex ORS -@end iftex -This is the output record separator. It is output at the end of every -@code{print} statement. Its default value is a string containing a -single newline character, which could be written as @code{"\n"}. -(@xref{Output Separators}.)@refill - -@item RS -@iftex -@vindex RS -@end iftex -This is @code{awk}'s input record separator. Its default value is a string -containing a single newline character, which means that an input record -consists of a single line of text. -(@xref{Records, ,How Input is Split into Records}.)@refill - -@item SUBSEP -@iftex -@vindex SUBSEP -@end iftex -@code{SUBSEP} is the subscript separator. It has the default value of -@code{"\034"}, and is used to separate the parts of the name of a -multi-dimensional array. Thus, if you access @code{foo[12,3]}, it -really accesses @code{foo["12\0343"]} -(@pxref{Multi-dimensional, ,Multi-dimensional Arrays}).@refill -@end table - -@node Auto-set, , User-modified, Built-in Variables -@section Built-in Variables that Convey Information - -This is a list of the variables that are set automatically by @code{awk} -on certain occasions so as to provide information to your program. - -@table @code -@item ARGC -@itemx ARGV -@iftex -@vindex ARGC -@vindex ARGV -@end iftex -The command-line arguments available to @code{awk} programs are stored in -an array called @code{ARGV}. @code{ARGC} is the number of command-line -arguments present. @xref{Command Line, ,Invoking @code{awk}}. -@code{ARGV} is indexed from zero to @w{@code{ARGC - 1}}. For example:@refill - -@example -awk 'BEGIN @{ - for (i = 0; i < ARGC; i++) - print ARGV[i] - @}' inventory-shipped BBS-list -@end example - -@noindent -In this example, @code{ARGV[0]} contains @code{"awk"}, @code{ARGV[1]} -contains @code{"inventory-shipped"}, and @code{ARGV[2]} contains -@code{"BBS-list"}. The value of @code{ARGC} is 3, one more than the -index of the last element in @code{ARGV} since the elements are numbered -from zero.@refill - -The names @code{ARGC} and @code{ARGV}, as well the convention of indexing -the array from 0 to @w{@code{ARGC - 1}}, are derived from the C language's -method of accessing command line arguments.@refill - -Notice that the @code{awk} program is not entered in @code{ARGV}. The -other special command line options, with their arguments, are also not -entered. But variable assignments on the command line @emph{are} -treated as arguments, and do show up in the @code{ARGV} array. - -Your program can alter @code{ARGC} and the elements of @code{ARGV}. -Each time @code{awk} reaches the end of an input file, it uses the next -element of @code{ARGV} as the name of the next input file. By storing a -different string there, your program can change which files are read. -You can use @code{"-"} to represent the standard input. By storing -additional elements and incrementing @code{ARGC} you can cause -additional files to be read. - -If you decrease the value of @code{ARGC}, that eliminates input files -from the end of the list. By recording the old value of @code{ARGC} -elsewhere, your program can treat the eliminated arguments as -something other than file names. - -To eliminate a file from the middle of the list, store the null string -(@code{""}) into @code{ARGV} in place of the file's name. As a -special feature, @code{awk} ignores file names that have been -replaced with the null string. - -@ignore -see getopt.awk in the examples... -@end ignore - -@item ARGIND -@vindex ARGIND -The index in @code{ARGV} of the current file being processed. -Every time @code{gawk} opens a new data file for processing, it sets -@code{ARGIND} to the index in @code{ARGV} of the file name. Thus, the -condition @samp{FILENAME == ARGV[ARGIND]} is always true. - -This variable is useful in file processing; it allows you to tell how far -along you are in the list of data files, and to distinguish between -multiple successive instances of the same filename on the command line. - -While you can change the value of @code{ARGIND} within your @code{awk} -program, @code{gawk} will automatically set it to a new value when the -next file is opened. - -This variable is a @code{gawk} extension; in other @code{awk} implementations -it is not special. - -@item ENVIRON -@vindex ENVIRON -This is an array that contains the values of the environment. The array -indices are the environment variable names; the values are the values of -the particular environment variables. For example, -@code{ENVIRON["HOME"]} might be @file{/u/close}. Changing this array -does not affect the environment passed on to any programs that -@code{awk} may spawn via redirection or the @code{system} function. -(In a future version of @code{gawk}, it may do so.) - -Some operating systems may not have environment variables. -On such systems, the array @code{ENVIRON} is empty. - -@item ERRNO -@iftex -@vindex ERRNO -@end iftex -If a system error occurs either doing a redirection for @code{getline}, -during a read for @code{getline}, or during a @code{close} operation, -then @code{ERRNO} will contain a string describing the error. - -This variable is a @code{gawk} extension; in other @code{awk} implementations -it is not special. - -@item FILENAME -@iftex -@vindex FILENAME -@end iftex -This is the name of the file that @code{awk} is currently reading. -If @code{awk} is reading from the standard input (in other words, -there are no files listed on the command line), -@code{FILENAME} is set to @code{"-"}. -@code{FILENAME} is changed each time a new file is read -(@pxref{Reading Files, ,Reading Input Files}).@refill - -@item FNR -@iftex -@vindex FNR -@end iftex -@code{FNR} is the current record number in the current file. @code{FNR} is -incremented each time a new record is read -(@pxref{Getline, ,Explicit Input with @code{getline}}). It is reinitialized -to 0 each time a new input file is started.@refill - -@item NF -@iftex -@vindex NF -@end iftex -@code{NF} is the number of fields in the current input record. -@code{NF} is set each time a new record is read, when a new field is -created, or when @code{$0} changes (@pxref{Fields, ,Examining Fields}).@refill - -@item NR -@iftex -@vindex NR -@end iftex -This is the number of input records @code{awk} has processed since -the beginning of the program's execution. -(@pxref{Records, ,How Input is Split into Records}). -@code{NR} is set each time a new record is read.@refill - -@item RLENGTH -@iftex -@vindex RLENGTH -@end iftex -@code{RLENGTH} is the length of the substring matched by the -@code{match} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). -@code{RLENGTH} is set by invoking the @code{match} function. Its value -is the length of the matched string, or @minus{}1 if no match was found.@refill - -@item RSTART -@iftex -@vindex RSTART -@end iftex -@code{RSTART} is the start-index in characters of the substring matched by the -@code{match} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). -@code{RSTART} is set by invoking the @code{match} function. Its value -is the position of the string where the matched substring starts, or 0 -if no match was found.@refill -@end table - -@node Command Line, Language History, Built-in Variables, Top -@c node-name, next, previous, up -@chapter Invoking @code{awk} -@cindex command line -@cindex invocation of @code{gawk} -@cindex arguments, command line -@cindex options, command line -@cindex long options -@cindex options, long - -There are two ways to run @code{awk}: with an explicit program, or with -one or more program files. Here are templates for both of them; items -enclosed in @samp{@r{[}@dots{}@r{]}} in these templates are optional. - -Besides traditional one-letter @sc{posix}-style options, @code{gawk} also -supports GNU long named options. - -@example -awk @r{[@var{POSIX or GNU style options}]} -f progfile @r{[@code{--}]} @var{file} @dots{} -awk @r{[@var{POSIX or GNU style options}]} @r{[@code{--}]} '@var{program}' @var{file} @dots{} -@end example - -@menu -* Options:: Command line options and their meanings. -* Other Arguments:: Input file names and variable assignments. -* AWKPATH Variable:: Searching directories for @code{awk} programs. -* Obsolete:: Obsolete Options and/or features. -* Undocumented:: Undocumented Options and Features. -@end menu - -@node Options, Other Arguments, Command Line, Command Line -@section Command Line Options - -Options begin with a minus sign, and consist of a single character. -GNU style long named options consist of two minus signs and -a keyword that can be abbreviated if the abbreviation allows the option -to be uniquely identified. If the option takes an argument, then the -keyword is immediately followed by an equals sign (@samp{=}) and the -argument's value. For brevity, the discussion below only refers to the -traditional short options; however the long and short options are -interchangeable in all contexts. - -Each long named option for @code{gawk} has a corresponding -@sc{posix}-style option. The options and their meanings are as follows: - -@table @code -@item -F @var{fs} -@itemx --field-separator=@var{fs} -@iftex -@cindex @code{-F} option -@end iftex -@cindex @code{--field-separator} option -Sets the @code{FS} variable to @var{fs} -(@pxref{Field Separators, ,Specifying how Fields are Separated}).@refill - -@item -f @var{source-file} -@itemx --file=@var{source-file} -@iftex -@cindex @code{-f} option -@end iftex -@cindex @code{--file} option -Indicates that the @code{awk} program is to be found in @var{source-file} -instead of in the first non-option argument. - -@item -v @var{var}=@var{val} -@itemx --assign=@var{var}=@var{val} -@cindex @samp{-v} option -@cindex @code{--assign} option -Sets the variable @var{var} to the value @var{val} @emph{before} -execution of the program begins. Such variable values are available -inside the @code{BEGIN} rule (see below for a fuller explanation). - -The @samp{-v} option can only set one variable, but you can use -it more than once, setting another variable each time, like this: -@samp{@w{-v foo=1} @w{-v bar=2}}. - -@item -W @var{gawk-opt} -@cindex @samp{-W} option -Following the @sc{posix} standard, options that are implementation -specific are supplied as arguments to the @samp{-W} option. With @code{gawk}, -these arguments may be separated by commas, or quoted and separated by -whitespace. Case is ignored when processing these options. These options -also have corresponding GNU style long named options. The following -@code{gawk}-specific options are available: - -@table @code -@item -W compat -@itemx --compat -@cindex @code{--compat} option -Specifies @dfn{compatibility mode}, in which the GNU extensions in -@code{gawk} are disabled, so that @code{gawk} behaves just like Unix -@code{awk}. -@xref{POSIX/GNU, ,Extensions in @code{gawk} not in POSIX @code{awk}}, -which summarizes the extensions. Also see -@ref{Compatibility Mode, ,Downward Compatibility and Debugging}.@refill - -@item -W copyleft -@itemx -W copyright -@itemx --copyleft -@itemx --copyright -@cindex @code{--copyleft} option -@cindex @code{--copyright} option -Print the short version of the General Public License. -This option may disappear in a future version of @code{gawk}. - -@item -W help -@itemx -W usage -@itemx --help -@itemx --usage -@cindex @code{--help} option -@cindex @code{--usage} option -Print a ``usage'' message summarizing the short and long style options -that @code{gawk} accepts, and then exit. - -@item -W lint -@itemx --lint -@cindex @code{--lint} option -Provide warnings about constructs that are dubious or non-portable to -other @code{awk} implementations. -Some warnings are issued when @code{gawk} first reads your program. Others -are issued at run-time, as your program executes. - -@item -W posix -@itemx --posix -@cindex @code{--posix} option -Operate in strict @sc{posix} mode. This disables all @code{gawk} -extensions (just like @code{-W compat}), and adds the following additional -restrictions: - -@itemize @bullet{} -@item -@code{\x} escape sequences are not recognized -(@pxref{Constants, ,Constant Expressions}).@refill - -@item -The synonym @code{func} for the keyword @code{function} is not -recognized (@pxref{Definition Syntax, ,Syntax of Function Definitions}). - -@item -The operators @samp{**} and @samp{**=} cannot be used in -place of @samp{^} and @samp{^=} (@pxref{Arithmetic Ops, ,Arithmetic Operators}, -and also @pxref{Assignment Ops, ,Assignment Expressions}).@refill - -@item -Specifying @samp{-Ft} on the command line does not set the value -of @code{FS} to be a single tab character -(@pxref{Field Separators, ,Specifying how Fields are Separated}).@refill -@end itemize - -Although you can supply both @samp{-W compat} and @samp{-W posix} on the -command line, @samp{-W posix} will take precedence. - -@item -W source=@var{program-text} -@itemx --source=@var{program-text} -@cindex @code{--source} option -Program source code is taken from the @var{program-text}. This option -allows you to mix @code{awk} source code in files with program source -code that you would enter on the command line. This is particularly useful -when you have library functions that you wish to use from your command line -programs (@pxref{AWKPATH Variable, ,The @code{AWKPATH} Environment Variable}). - -@item -W version -@itemx --version -@cindex @code{--version} option -Prints version information for this particular copy of @code{gawk}. -This is so you can determine if your copy of @code{gawk} is up to date -with respect to whatever the Free Software Foundation is currently -distributing. This option may disappear in a future version of @code{gawk}. -@end table - -@item -- -Signals the end of the command line options. The following arguments -are not treated as options even if they begin with @samp{-}. This -interpretation of @samp{--} follows the @sc{posix} argument parsing -conventions. - -This is useful if you have file names that start with @samp{-}, -or in shell scripts, if you have file names that will be specified -by the user which could start with @samp{-}. -@end table - -Any other options are flagged as invalid with a warning message, but -are otherwise ignored. - -In compatibility mode, as a special case, if the value of @var{fs} supplied -to the @samp{-F} option is @samp{t}, then @code{FS} is set to the tab -character (@code{"\t"}). This is only true for @samp{-W compat}, and not -for @samp{-W posix} -(@pxref{Field Separators, ,Specifying how Fields are Separated}).@refill - -If the @samp{-f} option is @emph{not} used, then the first non-option -command line argument is expected to be the program text. - -The @samp{-f} option may be used more than once on the command line. -If it is, @code{awk} reads its program source from all of the named files, as -if they had been concatenated together into one big file. This is -useful for creating libraries of @code{awk} functions. Useful functions -can be written once, and then retrieved from a standard place, instead -of having to be included into each individual program. You can still -type in a program at the terminal and use library functions, by specifying -@samp{-f /dev/tty}. @code{awk} will read a file from the terminal -to use as part of the @code{awk} program. After typing your program, -type @kbd{Control-d} (the end-of-file character) to terminate it. -(You may also use @samp{-f -} to read program source from the standard -input, but then you will not be able to also use the standard input as a -source of data.) - -Because it is clumsy using the standard @code{awk} mechanisms to mix source -file and command line @code{awk} programs, @code{gawk} provides the -@samp{--source} option. This does not require you to pre-empt the standard -input for your source code, and allows you to easily mix command line -and library source code -(@pxref{AWKPATH Variable, ,The @code{AWKPATH} Environment Variable}). - -If no @samp{-f} or @samp{--source} option is specified, then @code{gawk} -will use the first non-option command line argument as the text of the -program source code. - -@node Other Arguments, AWKPATH Variable, Options, Command Line -@section Other Command Line Arguments - -Any additional arguments on the command line are normally treated as -input files to be processed in the order specified. However, an -argument that has the form @code{@var{var}=@var{value}}, means to assign -the value @var{value} to the variable @var{var}---it does not specify a -file at all. - -@vindex ARGV -All these arguments are made available to your @code{awk} program in the -@code{ARGV} array (@pxref{Built-in Variables}). Command line options -and the program text (if present) are omitted from the @code{ARGV} -array. All other arguments, including variable assignments, are -included. - -The distinction between file name arguments and variable-assignment -arguments is made when @code{awk} is about to open the next input file. -At that point in execution, it checks the ``file name'' to see whether -it is really a variable assignment; if so, @code{awk} sets the variable -instead of reading a file. - -Therefore, the variables actually receive the specified values after all -previously specified files have been read. In particular, the values of -variables assigned in this fashion are @emph{not} available inside a -@code{BEGIN} rule -(@pxref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}), -since such rules are run before @code{awk} begins scanning the argument list. -The values given on the command line are processed for escape sequences -(@pxref{Constants, ,Constant Expressions}).@refill - -In some earlier implementations of @code{awk}, when a variable assignment -occurred before any file names, the assignment would happen @emph{before} -the @code{BEGIN} rule was executed. Some applications came to depend -upon this ``feature.'' When @code{awk} was changed to be more consistent, -the @samp{-v} option was added to accommodate applications that depended -upon this old behavior. - -The variable assignment feature is most useful for assigning to variables -such as @code{RS}, @code{OFS}, and @code{ORS}, which control input and -output formats, before scanning the data files. It is also useful for -controlling state if multiple passes are needed over a data file. For -example:@refill - -@cindex multiple passes over data -@cindex passes, multiple -@smallexample -awk 'pass == 1 @{ @var{pass 1 stuff} @} - pass == 2 @{ @var{pass 2 stuff} @}' pass=1 datafile pass=2 datafile -@end smallexample - -Given the variable assignment feature, the @samp{-F} option is not -strictly necessary. It remains for historical compatibility. - -@node AWKPATH Variable, Obsolete, Other Arguments, Command Line -@section The @code{AWKPATH} Environment Variable -@cindex @code{AWKPATH} environment variable -@cindex search path -@cindex directory search -@cindex path, search -@iftex -@cindex differences between @code{gawk} and @code{awk} -@end iftex - -The previous section described how @code{awk} program files can be named -on the command line with the @samp{-f} option. In some @code{awk} -implementations, you must supply a precise path name for each program -file, unless the file is in the current directory. - -But in @code{gawk}, if the file name supplied in the @samp{-f} option -does not contain a @samp{/}, then @code{gawk} searches a list of -directories (called the @dfn{search path}), one by one, looking for a -file with the specified name. - -The search path is actually a string consisting of directory names -separated by colons. @code{gawk} gets its search path from the -@code{AWKPATH} environment variable. If that variable does not exist, -@code{gawk} uses the default path, which is -@samp{.:/usr/lib/awk:/usr/local/lib/awk}. (Programs written by -system administrators should use an @code{AWKPATH} variable that -does not include the current directory, @samp{.}.)@refill - -The search path feature is particularly useful for building up libraries -of useful @code{awk} functions. The library files can be placed in a -standard directory that is in the default path, and then specified on -the command line with a short file name. Otherwise, the full file name -would have to be typed for each file. - -By combining the @samp{--source} and @samp{-f} options, your command line -@code{awk} programs can use facilities in @code{awk} library files. - -Path searching is not done if @code{gawk} is in compatibility mode. -This is true for both @samp{-W compat} and @samp{-W posix}. -@xref{Options, ,Command Line Options}. - -@strong{Note:} if you want files in the current directory to be found, -you must include the current directory in the path, either by writing -@file{.} as an entry in the path, or by writing a null entry in the -path. (A null entry is indicated by starting or ending the path with a -colon, or by placing two colons next to each other (@samp{::}).) If the -current directory is not included in the path, then files cannot be -found in the current directory. This path search mechanism is identical -to the shell's. -@c someday, @cite{The Bourne Again Shell}.... - -@node Obsolete, Undocumented, AWKPATH Variable, Command Line -@section Obsolete Options and/or Features - -@cindex deprecated options -@cindex obsolete options -@cindex deprecated features -@cindex obsolete features -This section describes features and/or command line options from the -previous release of @code{gawk} that are either not available in the -current version, or that are still supported but deprecated (meaning that -they will @emph{not} be in the next release). - -@c update this section for each release! - -For version 2.15 of @code{gawk}, the following command line options -from version 2.11.1 are no longer recognized. - -@table @samp -@ignore -@item -nostalgia -Use @samp{-W nostalgia} instead. -@end ignore - -@item -c -Use @samp{-W compat} instead. - -@item -V -Use @samp{-W version} instead. - -@item -C -Use @samp{-W copyright} instead. - -@item -a -@itemx -e -These options produce an ``unrecognized option'' error message but have -no effect on the execution of @code{gawk}. The @sc{posix} standard now -specifies traditional @code{awk} regular expressions for the @code{awk} utility. -@end table - -The public-domain version of @code{strftime} that is distributed with -@code{gawk} changed for the 2.14 release. The @samp{%V} conversion specifier -that used to generate the date in VMS format was changed to @samp{%v}. -This is because the @sc{posix} standard for the @code{date} utility now -specifies a @samp{%V} conversion specifier. -@xref{Time Functions, ,Functions for Dealing with Time Stamps}, for details. - -@node Undocumented, , Obsolete, Command Line -@section Undocumented Options and Features - -This section intentionally left blank. - -@c Read The Source, Luke! - -@ignore -@c If these came out in the Info file or TeX manual, then they wouldn't -@c be undocumented, would they? - -@code{gawk} has one undocumented option: - -@table @samp -@item -W nostalgia -Print the message @code{"awk: bailing out near line 1"} and dump core. -This option was inspired by the common behavior of very early versions of -Unix @code{awk}, and by a t--shirt. -@end table - -Early versions of @code{awk} used to not require any separator (either -a newline or @samp{;}) between the rules in @code{awk} programs. Thus, -it was common to see one-line programs like: - -@example -awk '@{ sum += $1 @} END @{ print sum @}' -@end example - -@code{gawk} actually supports this, but it is purposely undocumented -since it is considered bad style. The correct way to write such a program -is either - -@example -awk '@{ sum += $1 @} ; END @{ print sum @}' -@end example - -@noindent -or - -@example -awk '@{ sum += $1 @} - END @{ print sum @}' data -@end example - -@noindent -@xref{Statements/Lines, ,@code{awk} Statements versus Lines}, for a fuller -explanation.@refill - -As an accident of the implementation of the original Unix @code{awk}, if -a built-in function used @code{$0} as its default argument, it was possible -to call that function without the parentheses. In particular, it was -common practice to use the @code{length} function in this fashion. -For example, the pipeline: - -@example -echo abcdef | awk '@{ print length @}' -@end example - -@noindent -would print @samp{6}. - -For backwards compatibility with old programs, @code{gawk} supports -this usage, but only for the @code{length} function. New programs should -@emph{not} call the @code{length} function this way. In particular, -this usage will not be portable to other @sc{posix} compliant versions -of @code{awk}. It is also poor style. - -@end ignore - -@node Language History, Installation, Command Line, Top -@chapter The Evolution of the @code{awk} Language - -This manual describes the GNU implementation of @code{awk}, which is patterned -after the @sc{posix} specification. Many @code{awk} users are only familiar -with the original @code{awk} implementation in Version 7 Unix, which is also -the basis for the version in Berkeley Unix (through 4.3--Reno). This chapter -briefly describes the evolution of the @code{awk} language. - -@menu -* V7/S5R3.1:: The major changes between V7 and - System V Release 3.1. -* S5R4:: Minor changes between System V - Releases 3.1 and 4. -* POSIX:: New features from the @sc{posix} standard. -* POSIX/GNU:: The extensions in @code{gawk} - not in @sc{posix} @code{awk}. -@end menu - -@node V7/S5R3.1, S5R4, Language History, Language History -@section Major Changes between V7 and S5R3.1 - -The @code{awk} language evolved considerably between the release of -Version 7 Unix (1978) and the new version first made widely available in -System V Release 3.1 (1987). This section summarizes the changes, with -cross-references to further details. - -@itemize @bullet -@item -The requirement for @samp{;} to separate rules on a line -(@pxref{Statements/Lines, ,@code{awk} Statements versus Lines}). - -@item -User-defined functions, and the @code{return} statement -(@pxref{User-defined, ,User-defined Functions}). - -@item -The @code{delete} statement (@pxref{Delete, ,The @code{delete} Statement}). - -@item -The @code{do}-@code{while} statement -(@pxref{Do Statement, ,The @code{do}-@code{while} Statement}).@refill - -@item -The built-in functions @code{atan2}, @code{cos}, @code{sin}, @code{rand} and -@code{srand} (@pxref{Numeric Functions, ,Numeric Built-in Functions}). - -@item -The built-in functions @code{gsub}, @code{sub}, and @code{match} -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). - -@item -The built-in functions @code{close}, which closes an open file, and -@code{system}, which allows the user to execute operating system -commands (@pxref{I/O Functions, ,Built-in Functions for Input/Output}).@refill -@c Does the above verbiage prevents an overfull hbox? --mew, rjc 24jan1992 - -@item -The @code{ARGC}, @code{ARGV}, @code{FNR}, @code{RLENGTH}, @code{RSTART}, -and @code{SUBSEP} built-in variables (@pxref{Built-in Variables}). - -@item -The conditional expression using the operators @samp{?} and @samp{:} -(@pxref{Conditional Exp, ,Conditional Expressions}).@refill - -@item -The exponentiation operator @samp{^} -(@pxref{Arithmetic Ops, ,Arithmetic Operators}) and its assignment operator -form @samp{^=} (@pxref{Assignment Ops, ,Assignment Expressions}).@refill - -@item -C-compatible operator precedence, which breaks some old @code{awk} -programs (@pxref{Precedence, ,Operator Precedence (How Operators Nest)}). - -@item -Regexps as the value of @code{FS} -(@pxref{Field Separators, ,Specifying how Fields are Separated}), and as the -third argument to the @code{split} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}).@refill - -@item -Dynamic regexps as operands of the @samp{~} and @samp{!~} operators -(@pxref{Regexp Usage, ,How to Use Regular Expressions}). - -@item -Escape sequences (@pxref{Constants, ,Constant Expressions}) in regexps.@refill - -@item -The escape sequences @samp{\b}, @samp{\f}, and @samp{\r} -(@pxref{Constants, ,Constant Expressions}). - -@item -Redirection of input for the @code{getline} function -(@pxref{Getline, ,Explicit Input with @code{getline}}).@refill - -@item -Multiple @code{BEGIN} and @code{END} rules -(@pxref{BEGIN/END, ,@code{BEGIN} and @code{END} Special Patterns}).@refill - -@item -Simulated multi-dimensional arrays -(@pxref{Multi-dimensional, ,Multi-dimensional Arrays}).@refill -@end itemize - -@node S5R4, POSIX, V7/S5R3.1, Language History -@section Changes between S5R3.1 and S5R4 - -The System V Release 4 version of Unix @code{awk} added these features -(some of which originated in @code{gawk}): - -@itemize @bullet -@item -The @code{ENVIRON} variable (@pxref{Built-in Variables}). - -@item -Multiple @samp{-f} options on the command line -(@pxref{Command Line, ,Invoking @code{awk}}).@refill - -@item -The @samp{-v} option for assigning variables before program execution begins -(@pxref{Command Line, ,Invoking @code{awk}}).@refill - -@item -The @samp{--} option for terminating command line options. - -@item -The @samp{\a}, @samp{\v}, and @samp{\x} escape sequences -(@pxref{Constants, ,Constant Expressions}).@refill - -@item -A defined return value for the @code{srand} built-in function -(@pxref{Numeric Functions, ,Numeric Built-in Functions}). - -@item -The @code{toupper} and @code{tolower} built-in string functions -for case translation -(@pxref{String Functions, ,Built-in Functions for String Manipulation}).@refill - -@item -A cleaner specification for the @samp{%c} format-control letter in the -@code{printf} function -(@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}).@refill - -@item -The ability to dynamically pass the field width and precision (@code{"%*.*d"}) -in the argument list of the @code{printf} function -(@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}).@refill - -@item -The use of constant regexps such as @code{/foo/} as expressions, where -they are equivalent to use of the matching operator, as in @code{$0 ~ -/foo/} (@pxref{Constants, ,Constant Expressions}). -@end itemize - -@node POSIX, POSIX/GNU, S5R4, Language History -@section Changes between S5R4 and POSIX @code{awk} - -The @sc{posix} Command Language and Utilities standard for @code{awk} -introduced the following changes into the language: - -@itemize @bullet{} -@item -The use of @samp{-W} for implementation-specific options. - -@item -The use of @code{CONVFMT} for controlling the conversion of numbers -to strings (@pxref{Conversion, ,Conversion of Strings and Numbers}). - -@item -The concept of a numeric string, and tighter comparison rules to go -with it (@pxref{Comparison Ops, ,Comparison Expressions}). - -@item -More complete documentation of many of the previously undocumented -features of the language. -@end itemize - -@node POSIX/GNU, , POSIX, Language History -@section Extensions in @code{gawk} not in POSIX @code{awk} - -The GNU implementation, @code{gawk}, adds these features: - -@itemize @bullet -@item -The @code{AWKPATH} environment variable for specifying a path search for -the @samp{-f} command line option -(@pxref{Command Line, ,Invoking @code{awk}}).@refill - -@item -The various @code{gawk} specific features available via the @samp{-W} -command line option (@pxref{Command Line, ,Invoking @code{awk}}). - -@item -The @code{ARGIND} variable, that tracks the movement of @code{FILENAME} -through @code{ARGV}. (@pxref{Built-in Variables}). - -@item -The @code{ERRNO} variable, that contains the system error message when -@code{getline} returns @minus{}1, or when @code{close} fails. -(@pxref{Built-in Variables}). - -@item -The @code{IGNORECASE} variable and its effects -(@pxref{Case-sensitivity, ,Case-sensitivity in Matching}).@refill - -@item -The @code{FIELDWIDTHS} variable and its effects -(@pxref{Constant Size, ,Reading Fixed-width Data}).@refill - -@item -The @code{next file} statement for skipping to the next data file -(@pxref{Next File Statement, ,The @code{next file} Statement}).@refill - -@item -The @code{systime} and @code{strftime} built-in functions for obtaining -and printing time stamps -(@pxref{Time Functions, ,Functions for Dealing with Time Stamps}).@refill - -@item -The @file{/dev/stdin}, @file{/dev/stdout}, @file{/dev/stderr}, and -@file{/dev/fd/@var{n}} file name interpretation -(@pxref{Special Files, ,Standard I/O Streams}).@refill - -@item -The @samp{-W compat} option to turn off these extensions -(@pxref{Command Line, ,Invoking @code{awk}}).@refill - -@item -The @samp{-W posix} option for full @sc{posix} compliance -(@pxref{Command Line, ,Invoking @code{awk}}).@refill - -@end itemize - -@node Installation, Gawk Summary, Language History, Top -@chapter Installing @code{gawk} - -This chapter provides instructions for installing @code{gawk} on the -various platforms that are supported by the developers. The primary -developers support Unix (and one day, GNU), while the other ports were -contributed. The file @file{ACKNOWLEDGMENT} in the @code{gawk} -distribution lists the electronic mail addresses of the people who did -the respective ports.@refill - -@menu -* Gawk Distribution:: What is in the @code{gawk} distribution. -* Unix Installation:: Installing @code{gawk} under various versions - of Unix. -* VMS Installation:: Installing @code{gawk} on VMS. -* MS-DOS Installation:: Installing @code{gawk} on MS-DOS. -* Atari Installation:: Installing @code{gawk} on the Atari ST. -@end menu - -@node Gawk Distribution, Unix Installation, Installation, Installation -@section The @code{gawk} Distribution - -This section first describes how to get and extract the @code{gawk} -distribution, and then discusses what is in the various files and -subdirectories. - -@menu -* Extracting:: How to get and extract the distribution. -* Distribution contents:: What is in the distribution. -@end menu - -@node Extracting, Distribution contents, Gawk Distribution, Gawk Distribution -@subsection Getting the @code{gawk} Distribution - -@cindex getting gawk -@cindex anonymous ftp -@cindex anonymous uucp -@cindex ftp, anonymous -@cindex uucp, anonymous -@code{gawk} is distributed as a @code{tar} file compressed with the -GNU Zip program, @code{gzip}. You can -get it via anonymous @code{ftp} to the Internet host @code{prep.ai.mit.edu}. -Like all GNU software, it will be archived at other well known systems, -from which it will be possible to use some sort of anonymous @code{uucp} to -obtain the distribution as well. -You can also order @code{gawk} on tape or CD-ROM directly from the -Free Software Foundation. (The address is on the copyright page.) -Doing so directly contributes to the support of the foundation and to -the production of more free software. - -Once you have the distribution (for example, -@file{gawk-2.15.0.tar.z}), first use @code{gzip} to expand the -file, and then use @code{tar} to extract it. You can use the following -pipeline to produce the @code{gawk} distribution: - -@example -# Under System V, add 'o' to the tar flags -gzip -d -c gawk-2.15.0.tar.z | tar -xvpf - -@end example - -@noindent -This will create a directory named @file{gawk-2.15} in the current -directory. - -The distribution file name is of the form @file{gawk-2.15.@var{n}.tar.Z}. -The @var{n} represents a @dfn{patchlevel}, meaning that minor bugs have -been fixed in the major release. The current patchlevel is 0, but when -retrieving distributions, you should get the version with the highest -patchlevel.@refill - -If you are not on a Unix system, you will need to make other arrangements -for getting and extracting the @code{gawk} distribution. You should consult -a local expert. - -@node Distribution contents, , Extracting, Gawk Distribution -@subsection Contents of the @code{gawk} Distribution - -@code{gawk} has a number of C source files, documentation files, -subdirectories and files related to the configuration process -(@pxref{Unix Installation, ,Compiling and Installing @code{gawk} on Unix}), -and several subdirectories related to different, non-Unix, -operating systems.@refill - -@table @asis -@item various @samp{.c}, @samp{.y}, and @samp{.h} files - -The C and YACC source files are the actual @code{gawk} source code. -@end table - -@table @file -@item README -@itemx README.VMS -@itemx README.dos -@itemx README.rs6000 -@itemx README.ultrix -Descriptive files: @file{README} for @code{gawk} under Unix, and the -rest for the various hardware and software combinations. - -@item PORTS -A list of systems to which @code{gawk} has been ported, and which -have successfully run the test suite. - -@item ACKNOWLEDGMENT -A list of the people who contributed major parts of the code or documentation. - -@item NEWS -A list of changes to @code{gawk} since the last release or patch. - -@item COPYING -The GNU General Public License. - -@item FUTURES -A brief list of features and/or changes being contemplated for future -releases, with some indication of the time frame for the feature, based -on its difficulty. - -@item LIMITATIONS -A list of those factors that limit @code{gawk}'s performance. -Most of these depend on the hardware or operating system software, and -are not limits in @code{gawk} itself.@refill - -@item PROBLEMS -A file describing known problems with the current release. - -@item gawk.1 -The @code{troff} source for a manual page describing @code{gawk}. - -@item gawk.texinfo -@ifinfo -The @code{texinfo} source file for this Info file. -It should be processed with @TeX{} to produce a printed manual, and -with @code{makeinfo} to produce the Info file.@refill -@end ifinfo -@iftex -The @code{texinfo} source file for this manual. -It should be processed with @TeX{} to produce a printed manual, and -with @code{makeinfo} to produce the Info file.@refill -@end iftex - -@item Makefile.in -@itemx config -@itemx config.in -@itemx configure -@itemx missing -@itemx mungeconf -These files and subdirectories are used when configuring @code{gawk} -for various Unix systems. They are explained in detail in -@ref{Unix Installation, ,Compiling and Installing @code{gawk} on Unix}.@refill - -@item atari -Files needed for building @code{gawk} on an Atari ST. -@xref{Atari Installation, ,Installing @code{gawk} on the Atari ST}, for details. - -@item pc -Files needed for building @code{gawk} under MS-DOS. -@xref{MS-DOS Installation, ,Installing @code{gawk} on MS-DOS}, for details. - -@item vms -Files needed for building @code{gawk} under VMS. -@xref{VMS Installation, ,Compiling Installing and Running @code{gawk} on VMS}, for details. - -@item test -Many interesting @code{awk} programs, provided as a test suite for -@code{gawk}. You can use @samp{make test} from the top level @code{gawk} -directory to run your version of @code{gawk} against the test suite. -@c There are many programs here that are useful in their own right. -If @code{gawk} successfully passes @samp{make test} then you can -be confident of a successful port.@refill -@end table - -@node Unix Installation, VMS Installation, Gawk Distribution, Installation -@section Compiling and Installing @code{gawk} on Unix - -Often, you can compile and install @code{gawk} by typing only two -commands. However, if you do not use a supported system, you may need -to configure @code{gawk} for your system yourself. - -@menu -* Quick Installation:: Compiling @code{gawk} on a - supported Unix version. -* Configuration Philosophy:: How it's all supposed to work. -* New Configurations:: What to do if there is no supplied - configuration for your system. -@end menu - -@node Quick Installation, Configuration Philosophy, Unix Installation, Unix Installation -@subsection Compiling @code{gawk} for a Supported Unix Version - -@cindex installation, unix -After you have extracted the @code{gawk} distribution, @code{cd} -to @file{gawk-2.15}. Look in the @file{config} subdirectory for a -file that matches your hardware/software combination. In general, -only the software is relevant; for example @code{sunos41} is used -for SunOS 4.1, on both Sun 3 and Sun 4 hardware.@refill - -If you find such a file, run the command: - -@example -# assume you have SunOS 4.1 -./configure sunos41 -@end example - -This produces a @file{Makefile} and @file{config.h} tailored to your -system. You may wish to edit the @file{Makefile} to use a different -C compiler, such as @code{gcc}, the GNU C compiler, if you have it. -You may also wish to change the @code{CFLAGS} variable, which controls -the command line options that are passed to the C compiler (such as -optimization levels, or compiling for debugging).@refill - -After you have configured @file{Makefile} and @file{config.h}, type: - -@example -make -@end example - -@noindent -and shortly thereafter, you should have an executable version of @code{gawk}. -That's all there is to it! - -@node Configuration Philosophy, New Configurations, Quick Installation, Unix Installation -@subsection The Configuration Process - -(This section is of interest only if you know something about using the -C language and the Unix operating system.) - -The source code for @code{gawk} generally attempts to adhere to industry -standards wherever possible. This means that @code{gawk} uses library -routines that are specified by the @sc{ansi} C standard and by the @sc{posix} -operating system interface standard. When using an @sc{ansi} C compiler, -function prototypes are provided to help improve the compile-time checking. - -Many older Unix systems do not support all of either the @sc{ansi} or the -@sc{posix} standards. The @file{missing} subdirectory in the @code{gawk} -distribution contains replacement versions of those subroutines that are -most likely to be missing. - -The @file{config.h} file that is created by the @code{configure} program -contains definitions that describe features of the particular operating -system where you are attempting to compile @code{gawk}. For the most -part, it lists which standard subroutines are @emph{not} available. -For example, if your system lacks the @samp{getopt} routine, then -@samp{GETOPT_MISSING} would be defined. - -@file{config.h} also defines constants that describe facts about your -variant of Unix. For example, there may not be an @samp{st_blksize} -element in the @code{stat} structure. In this case @samp{BLKSIZE_MISSING} -would be defined. - -Based on the list in @file{config.h} of standard subroutines that are -missing, @file{missing.c} will do a @samp{#include} of the appropriate -file(s) from the @file{missing} subdirectory.@refill - -Conditionally compiled code in the other source files relies on the -other definitions in the @file{config.h} file. - -Besides creating @file{config.h}, @code{configure} produces a @file{Makefile} -from @file{Makefile.in}. There are a number of lines in @file{Makefile.in} -that are system or feature specific. For example, there is line that begins -with @samp{##MAKE_ALLOCA_C##}. This is normally a comment line, since -it starts with @samp{#}. If a configuration file has @samp{MAKE_ALLOCA_C} -in it, then @code{configure} will delete the @samp{##MAKE_ALLOCA_C##} -from the beginning of the line. This will enable the rules in the -@file{Makefile} that use a C version of @samp{alloca}. There are several -similar features that work in this fashion.@refill - -@node New Configurations, , Configuration Philosophy, Unix Installation -@subsection Configuring @code{gawk} for a New System - -(This section is of interest only if you know something about using the -C language and the Unix operating system, and if you have to install -@code{gawk} on a system that is not supported by the @code{gawk} distribution. -If you are a C or Unix novice, get help from a local expert.) - -If you need to configure @code{gawk} for a Unix system that is not -supported in the distribution, first see -@ref{Configuration Philosophy, ,The Configuration Process}. -Then, copy @file{config.in} to @file{config.h}, and copy -@file{Makefile.in} to @file{Makefile}.@refill - -Next, edit both files. Both files are liberally commented, and the -necessary changes should be straightforward. - -While editing @file{config.h}, you need to determine what library -routines you do or do not have by consulting your system documentation, or -by perusing your actual libraries using the @code{ar} or @code{nm} utilities. -In the worst case, simply do not define @emph{any} of the macros for missing -subroutines. When you compile @code{gawk}, the final link-editing step -will fail. The link editor will provide you with a list of unresolved external -references---these are the missing subroutines. Edit @file{config.h} again -and recompile, and you should be set.@refill - -Editing the @file{Makefile} should also be straightforward. Enable or -disable the lines that begin with @samp{##MAKE_@var{whatever}##}, as -appropriate. Select the correct C compiler and @code{CFLAGS} for it. -Then run @code{make}. - -Getting a correct configuration is likely to be an iterative process. -Do not be discouraged if it takes you several tries. If you have no -luck whatsoever, please report your system type, and the steps you took. -Once you do have a working configuration, please send it to the maintainers -so that support for your system can be added to the official release. - -@xref{Bugs, ,Reporting Problems and Bugs}, for information on how to report -problems in configuring @code{gawk}. You may also use the same mechanisms -for sending in new configurations.@refill - -@node VMS Installation, MS-DOS Installation, Unix Installation, Installation -@section Compiling, Installing, and Running @code{gawk} on VMS - -@c based on material from -@c Pat Rankin <rankin@eql.caltech.edu> - -@cindex installation, vms -This section describes how to compile and install @code{gawk} under VMS. - -@menu -* VMS Compilation:: How to compile @code{gawk} under VMS. -* VMS Installation Details:: How to install @code{gawk} under VMS. -* VMS Running:: How to run @code{gawk} under VMS. -* VMS POSIX:: Alternate instructions for VMS POSIX. -@end menu - -@node VMS Compilation, VMS Installation Details, VMS Installation, VMS Installation -@subsection Compiling @code{gawk} under VMS - -To compile @code{gawk} under VMS, there is a @code{DCL} command procedure that -will issue all the necessary @code{CC} and @code{LINK} commands, and there is -also a @file{Makefile} for use with the @code{MMS} utility. From the source -directory, use either - -@smallexample -$ @@[.VMS]VMSBUILD.COM -@end smallexample - -@noindent -or - -@smallexample -$ MMS/DESCRIPTION=[.VMS]DECSRIP.MMS GAWK -@end smallexample - -Depending upon which C compiler you are using, follow one of the sets -of instructions in this table: - -@table @asis -@item VAX C V3.x -Use either @file{vmsbuild.com} or @file{descrip.mms} as is. These use -@code{CC/OPTIMIZE=NOLINE}, which is essential for Version 3.0. - -@item VAX C V2.x -You must have Version 2.3 or 2.4; older ones won't work. Edit either -@file{vmsbuild.com} or @file{descrip.mms} according to the comments in them. -For @file{vmsbuild.com}, this just entails removing two @samp{!} delimiters. -Also edit @file{config.h} (which is a copy of file @file{[.config]vms-conf.h}) -and comment out or delete the two lines @samp{#define __STDC__ 0} and -@samp{#define VAXC_BUILTINS} near the end.@refill - -@item GNU C -Edit @file{vmsbuild.com} or @file{descrip.mms}; the changes are different -from those for VAX C V2.x, but equally straightforward. No changes to -@file{config.h} should be needed. - -@item DEC C -Edit @file{vmsbuild.com} or @file{descrip.mms} according to their comments. -No changes to @file{config.h} should be needed. -@end table - -@code{gawk} 2.15 has been tested under VAX/VMS 5.5-1 using VAX C V3.2, -GNU C 1.40 and 2.3. It should work without modifications for VMS V4.6 and up. - -@node VMS Installation Details, VMS Running, VMS Compilation, VMS Installation -@subsection Installing @code{gawk} on VMS - -To install @code{gawk}, all you need is a ``foreign'' command, which is -a @code{DCL} symbol whose value begins with a dollar sign. - -@smallexample -$ GAWK :== $device:[directory]GAWK -@end smallexample - -@noindent -(Substitute the actual location of @code{gawk.exe} for -@samp{device:[directory]}.) The symbol should be placed in the -@file{login.com} of any user who wishes to run @code{gawk}, -so that it will be defined every time the user logs on. -Alternatively, the symbol may be placed in the system-wide -@file{sylogin.com} procedure, which will allow all users -to run @code{gawk}.@refill - -Optionally, the help entry can be loaded into a VMS help library: - -@smallexample -$ LIBRARY/HELP SYS$HELP:HELPLIB [.VMS]GAWK.HLP -@end smallexample - -@noindent -(You may want to substitute a site-specific help library rather than -the standard VMS library @samp{HELPLIB}.) After loading the help text, - -@c this is so tiny, but `should' be smallexample for consistency sake... -@c I didn't because it was so short. --mew 29jan1992 -@example -$ HELP GAWK -@end example - -@noindent -will provide information about both the @code{gawk} implementation and the -@code{awk} programming language. - -The logical name @samp{AWK_LIBRARY} can designate a default location -for @code{awk} program files. For the @samp{-f} option, if the specified -filename has no device or directory path information in it, @code{gawk} -will look in the current directory first, then in the directory specified -by the translation of @samp{AWK_LIBRARY} if the file was not found. -If after searching in both directories, the file still is not found, -then @code{gawk} appends the suffix @samp{.awk} to the filename and the -file search will be re-tried. If @samp{AWK_LIBRARY} is not defined, that -portion of the file search will fail benignly.@refill - -@node VMS Running, VMS POSIX, VMS Installation Details, VMS Installation -@subsection Running @code{gawk} on VMS - -Command line parsing and quoting conventions are significantly different -on VMS, so examples in this manual or from other sources often need minor -changes. They @emph{are} minor though, and all @code{awk} programs -should run correctly. - -Here are a couple of trivial tests: - -@smallexample -$ gawk -- "BEGIN @{print ""Hello, World!""@}" -$ gawk -"W" version ! could also be -"W version" or "-W version" -@end smallexample - -@noindent -Note that upper-case and mixed-case text must be quoted. - -The VMS port of @code{gawk} includes a @code{DCL}-style interface in addition -to the original shell-style interface (see the help entry for details). -One side-effect of dual command line parsing is that if there is only a -single parameter (as in the quoted string program above), the command -becomes ambiguous. To work around this, the normally optional @samp{--} -flag is required to force Unix style rather than @code{DCL} parsing. If any -other dash-type options (or multiple parameters such as data files to be -processed) are present, there is no ambiguity and @samp{--} can be omitted. - -The default search path when looking for @code{awk} program files specified -by the @samp{-f} option is @code{"SYS$DISK:[],AWK_LIBRARY:"}. The logical -name @samp{AWKPATH} can be used to override this default. The format -of @samp{AWKPATH} is a comma-separated list of directory specifications. -When defining it, the value should be quoted so that it retains a single -translation, and not a multi-translation @code{RMS} searchlist. - -@node VMS POSIX, , VMS Running, VMS Installation -@subsection Building and using @code{gawk} under VMS POSIX - -Ignore the instructions above, although @file{vms/gawk.hlp} should still -be made available in a help library. Make sure that the two scripts, -@file{configure} and @file{mungeconf}, are executable; use @samp{chmod +x} -on them if necessary. Then execute the following commands: - -@smallexample -$ POSIX -psx> configure vms-posix -psx> make awktab.c gawk -@end smallexample - -@noindent -The first command will construct files @file{config.h} and @file{Makefile} -out of templates. The second command will compile and link @code{gawk}. -Due to a @code{make} bug in VMS POSIX V1.0 and V1.1, -the file @file{awktab.c} must be given as an explicit target or it will -not be built and the final link step will fail. Ignore the warning -@samp{"Could not find lib m in lib list"}; it is harmless, caused by the -explicit use of @samp{-lm} as a linker option which is not needed -under VMS POSIX. Under V1.1 (but not V1.0) a problem with the @code{yacc} -skeleton @file{/etc/yyparse.c} will cause a compiler warning for -@file{awktab.c}, followed by a linker warning about compilation warnings -in the resulting object module. These warnings can be ignored.@refill - -Once built, @code{gawk} will work like any other shell utility. Unlike -the normal VMS port of @code{gawk}, no special command line manipulation is -needed in the VMS POSIX environment. - -@node MS-DOS Installation, Atari Installation, VMS Installation, Installation -@section Installing @code{gawk} on MS-DOS - -@cindex installation, ms-dos -The first step is to get all the files in the @code{gawk} distribution -onto your PC. Move all the files from the @file{pc} directory into -the main directory where the other files are. Edit the file -@file{make.bat} so that it will be an acceptable MS-DOS batch file. -This means making sure that all lines are terminated with the ASCII -carriage return and line feed characters. -restrictions. - -@code{gawk} has only been compiled with version 5.1 of the Microsoft -C compiler. The file @file{make.bat} from the @file{pc} directory -assumes that you have this compiler. - -Copy the file @file{setargv.obj} from the library directory where it -resides to the @code{gawk} source code directory. - -Run @file{make.bat}. This will compile @code{gawk} for you, and link it. -That's all there is to it! - -@node Atari Installation, , MS-DOS Installation, Installation -@section Installing @code{gawk} on the Atari ST - -@c based on material from -@c Michal Jaegermann <ntomczak@vm.ucs.ualberta.ca> - -@cindex installation, atari -This section assumes that you are running TOS. It applies to other Atari -models (STe, TT) as well. - -In order to use @code{gawk}, you need to have a shell, either text or -graphics, that does not map all the characters of a command line to -upper case. Maintaining case distinction in option flags is very -important (@pxref{Command Line, ,Invoking @code{awk}}). Popular shells -like @code{gulam} or @code{gemini} will work, as will newer versions of -@code{desktop}. Support for I/O redirection is necessary to make it easy -to import @code{awk} programs from other environments. Pipes are nice to have, -but not vital. - -If you have received an executable version of @code{gawk}, place it, -as usual, anywhere in your @code{PATH} where your shell will find it. - -While executing, @code{gawk} creates a number of temporary files. -@code{gawk} looks for either of the environment variables @code{TEMP} -or @code{TMPDIR}, in that order. If either one is found, its value -is assumed to be a directory for temporary files. This directory -must exist, and if you can spare the memory, it is a good idea to -put it on a @sc{ram} drive. If neither @code{TEMP} nor @code{TMPDIR} -are found, then @code{gawk} uses the current directory for its -temporary files. - -The ST version of @code{gawk} searches for its program files as -described in @ref{AWKPATH Variable, ,The @code{AWKPATH} Environment Variable}. -On the ST, the default value for the @code{AWKPATH} variable is -@code{@w{".,c:\lib\awk,c:\gnu\lib\awk"}}. -The search path can be modified by explicitly setting @code{AWKPATH} to -whatever you wish. Note that colons cannot be used on the ST to separate -elements in the @code{AWKPATH} variable, since they have another, reserved, -meaning. Instead, you must use a comma to separate elements in the path. -If you are recompiling @code{gawk} on the ST, then you can choose a new -default search path, by setting the value of @samp{DEFPATH} in the file -@file{...\config\atari}. You may choose a different separator character -by setting the value of @samp{ENVSEP} in the same file. The new values will -be used when creating the header file @file{config.h}.@refill - -@ignore -As a last resort, small -adjustments can be made directly on the executable version of @code{gawk} -using a binary editor.@refill -@end ignore - -Although @code{awk} allows great flexibility in doing I/O redirections -from within a program, this facility should be used with care on the ST. -In some circumstances the OS routines for file handle pool processing -lose track of certain events, causing the computer to crash, and requiring -a reboot. Often a warm reboot is sufficient. Fortunately, this happens -infrequently, and in rather esoteric situations. In particular, avoid -having one part of an @code{awk} program using @code{print} -statements explicitly redirected to @code{"/dev/stdout"}, while other -@code{print} statements use the default standard output, and a -calling shell has redirected standard output to a file.@refill -@c whew! - -When @code{gawk} is compiled with the ST version of @code{gcc} and its -usual libraries, it will accept both @samp{/} and @samp{\} as path separators. -While this is convenient, it should be remembered that this removes one, -technically legal, character (@samp{/}) from your file names, and that -it may create problems for external programs, called via the @code{system()} -function, which may not support this convention. Whenever it is possible -that a file created by @code{gawk} will be used by some other program, -use only backslashes. Also remember that in @code{awk}, backslashes in -strings have to be doubled in order to get literal backslashes. - -The initial port of @code{gawk} to the ST was done with @code{gcc}. -If you wish to recompile @code{gawk} from scratch, you will need to use -a compiler that accepts @sc{ansi} standard C (such as @code{gcc}, Turbo C, -or Prospero C). If @code{sizeof(int) != @w{sizeof(int *)}}, the correctness -of the generated code depends heavily on the fact that all function calls -have function prototypes in the current scope. If your compiler does -not accept function prototypes, you will probably have to add a -number of casts to the code.@refill - -If you are using @code{gcc}, make sure that you have up-to-date libraries. -Older versions have problems with some library functions (@code{atan2()}, -@code{strftime()}, the @samp{%g} conversion in @code{sprintf()}) which -may affect the operation of @code{gawk}. - -In the @file{atari} subdirectory of the @code{gawk} distribution is -a version of the @code{system()} function that has been tested with -@code{gulam} and @code{msh}; it should work with other shells as well. -With @code{gulam}, it passes the string to be executed without spawning -an extra copy of a shell. It is possible to replace this version of -@code{system()} with a similar function from a library or from some other -source if that version would be a better choice for the shell you prefer. - -The files needed to recompile @code{gawk} on the ST can be found in -the @file{atari} directory. The provided files and instructions below -assume that you have the GNU C compiler (@code{gcc}), the @code{gulam} shell, -and an ST version of @code{sed}. The @file{Makefile} is set up to use -@file{byacc} as a @file{yacc} replacement. With a different set of tools some -adjustments and/or editing will be needed.@refill - -@code{cd} to the @file{atari} directory. Copy @file{Makefile.st} to -@file{makefile} in the source (parent) directory. Possibly adjust -@file{../config/atari} to suit your system. Execute the script @file{mkconf.g} -which will create the header file @file{../config.h}. Go back to the source -directory. If you are not using @code{gcc}, check the file @file{missing.c}. -It may be necessary to change forward slashes in the references to files -from the @file{atari} subdirectory into backslashes. Type @code{make} and -enjoy.@refill - -Compilation with @code{gcc} of some of the bigger modules, like -@file{awk_tab.c}, may require a full four megabytes of memory. On smaller -machines you would need to cut down on optimizations, or you would have to -switch to another, less memory hungry, compiler.@refill - -@node Gawk Summary, Sample Program, Installation, Top -@appendix @code{gawk} Summary - -This appendix provides a brief summary of the @code{gawk} command line and the -@code{awk} language. It is designed to serve as ``quick reference.'' It is -therefore terse, but complete. - -@menu -* Command Line Summary:: Recapitulation of the command line. -* Language Summary:: A terse review of the language. -* Variables/Fields:: Variables, fields, and arrays. -* Rules Summary:: Patterns and Actions, and their - component parts. -* Functions Summary:: Defining and calling functions. -* Historical Features:: Some undocumented but supported ``features''. -@end menu - -@node Command Line Summary, Language Summary, Gawk Summary, Gawk Summary -@appendixsec Command Line Options Summary - -The command line consists of options to @code{gawk} itself, the -@code{awk} program text (if not supplied via the @samp{-f} option), and -values to be made available in the @code{ARGC} and @code{ARGV} -predefined @code{awk} variables: - -@example -awk @r{[@var{POSIX or GNU style options}]} -f source-file @r{[@code{--}]} @var{file} @dots{} -awk @r{[@var{POSIX or GNU style options}]} @r{[@code{--}]} '@var{program}' @var{file} @dots{} -@end example - -The options that @code{gawk} accepts are: - -@table @code -@item -F @var{fs} -@itemx --field-separator=@var{fs} -Use @var{fs} for the input field separator (the value of the @code{FS} -predefined variable). - -@item -f @var{program-file} -@itemx --file=@var{program-file} -Read the @code{awk} program source from the file @var{program-file}, instead -of from the first command line argument. - -@item -v @var{var}=@var{val} -@itemx --assign=@var{var}=@var{val} -Assign the variable @var{var} the value @var{val} before program execution -begins. - -@item -W compat -@itemx --compat -Specifies compatibility mode, in which @code{gawk} extensions are turned -off. - -@item -W copyleft -@itemx -W copyright -@itemx --copyleft -@itemx --copyright -Print the short version of the General Public License on the error -output. This option may disappear in a future version of @code{gawk}. - -@item -W help -@itemx -W usage -@itemx --help -@itemx --usage -Print a relatively short summary of the available options on the error output. - -@item -W lint -@itemx --lint -Give warnings about dubious or non-portable @code{awk} constructs. - -@item -W posix -@itemx --posix -Specifies @sc{posix} compatibility mode, in which @code{gawk} extensions -are turned off and additional restrictions apply. - -@item -W source=@var{program-text} -@itemx --source=@var{program-text} -Use @var{program-text} as @code{awk} program source code. This option allows -mixing command line source code with source code from files, and is -particularly useful for mixing command line programs with library functions. - -@item -W version -@itemx --version -Print version information for this particular copy of @code{gawk} on the error -output. This option may disappear in a future version of @code{gawk}. - -@item -- -Signal the end of options. This is useful to allow further arguments to the -@code{awk} program itself to start with a @samp{-}. This is mainly for -consistency with the argument parsing conventions of @sc{posix}. -@end table - -Any other options are flagged as invalid, but are otherwise ignored. -@xref{Command Line, ,Invoking @code{awk}}, for more details. - -@node Language Summary, Variables/Fields, Command Line Summary, Gawk Summary -@appendixsec Language Summary - -An @code{awk} program consists of a sequence of pattern-action statements -and optional function definitions. - -@example -@var{pattern} @{ @var{action statements} @} - -function @var{name}(@var{parameter list}) @{ @var{action statements} @} -@end example - -@code{gawk} first reads the program source from the -@var{program-file}(s) if specified, or from the first non-option -argument on the command line. The @samp{-f} option may be used multiple -times on the command line. @code{gawk} reads the program text from all -the @var{program-file} files, effectively concatenating them in the -order they are specified. This is useful for building libraries of -@code{awk} functions, without having to include them in each new -@code{awk} program that uses them. To use a library function in a file -from a program typed in on the command line, specify @samp{-f /dev/tty}; -then type your program, and end it with a @kbd{Control-d}. -@xref{Command Line, ,Invoking @code{awk}}.@refill - -The environment variable @code{AWKPATH} specifies a search path to use -when finding source files named with the @samp{-f} option. The default -path, which is -@samp{.:/usr/lib/awk:/usr/local/lib/awk} is used if @code{AWKPATH} is not set. -If a file name given to the @samp{-f} option contains a @samp{/} character, -no path search is performed. -@xref{AWKPATH Variable, ,The @code{AWKPATH} Environment Variable}, -for a full description of the @code{AWKPATH} environment variable.@refill - -@code{gawk} compiles the program into an internal form, and then proceeds to -read each file named in the @code{ARGV} array. If there are no files named -on the command line, @code{gawk} reads the standard input. - -If a ``file'' named on the command line has the form -@samp{@var{var}=@var{val}}, it is treated as a variable assignment: the -variable @var{var} is assigned the value @var{val}. -If any of the files have a value that is the null string, that -element in the list is skipped.@refill - -For each line in the input, @code{gawk} tests to see if it matches any -@var{pattern} in the @code{awk} program. For each pattern that the line -matches, the associated @var{action} is executed. - -@node Variables/Fields, Rules Summary, Language Summary, Gawk Summary -@appendixsec Variables and Fields - -@code{awk} variables are dynamic; they come into existence when they are -first used. Their values are either floating-point numbers or strings. -@code{awk} also has one-dimension arrays; multiple-dimensional arrays -may be simulated. There are several predefined variables that -@code{awk} sets as a program runs; these are summarized below. - -@menu -* Fields Summary:: Input field splitting. -* Built-in Summary:: @code{awk}'s built-in variables. -* Arrays Summary:: Using arrays. -* Data Type Summary:: Values in @code{awk} are numbers or strings. -@end menu - -@node Fields Summary, Built-in Summary, Variables/Fields, Variables/Fields -@appendixsubsec Fields - -As each input line is read, @code{gawk} splits the line into -@var{fields}, using the value of the @code{FS} variable as the field -separator. If @code{FS} is a single character, fields are separated by -that character. Otherwise, @code{FS} is expected to be a full regular -expression. In the special case that @code{FS} is a single blank, -fields are separated by runs of blanks and/or tabs. Note that the value -of @code{IGNORECASE} (@pxref{Case-sensitivity, ,Case-sensitivity in Matching}) -also affects how fields are split when @code{FS} is a regular expression.@refill - -Each field in the input line may be referenced by its position, @code{$1}, -@code{$2}, and so on. @code{$0} is the whole line. The value of a field may -be assigned to as well. Field numbers need not be constants: - -@example -n = 5 -print $n -@end example - -@noindent -prints the fifth field in the input line. The variable @code{NF} is set to -the total number of fields in the input line. - -References to nonexistent fields (i.e., fields after @code{$NF}) return -the null-string. However, assigning to a nonexistent field (e.g., -@code{$(NF+2) = 5}) increases the value of @code{NF}, creates any -intervening fields with the null string as their value, and causes the -value of @code{$0} to be recomputed, with the fields being separated by -the value of @code{OFS}.@refill - -@xref{Reading Files, ,Reading Input Files}, for a full description of the -way @code{awk} defines and uses fields. - -@node Built-in Summary, Arrays Summary, Fields Summary, Variables/Fields -@appendixsubsec Built-in Variables - -@code{awk}'s built-in variables are: - -@table @code -@item ARGC -The number of command line arguments (not including options or the -@code{awk} program itself). - -@item ARGIND -The index in @code{ARGV} of the current file being processed. -It is always true that @samp{FILENAME == ARGV[ARGIND]}. - -@item ARGV -The array of command line arguments. The array is indexed from 0 to -@code{ARGC} @minus{} 1. Dynamically changing the contents of @code{ARGV} -can control the files used for data.@refill - -@item CONVFMT -The conversion format to use when converting numbers to strings. - -@item FIELDWIDTHS -A space separated list of numbers describing the fixed-width input data. - -@item ENVIRON -An array containing the values of the environment variables. The array -is indexed by variable name, each element being the value of that -variable. Thus, the environment variable @code{HOME} would be in -@code{ENVIRON["HOME"]}. Its value might be @file{/u/close}. - -Changing this array does not affect the environment seen by programs -which @code{gawk} spawns via redirection or the @code{system} function. -(This may change in a future version of @code{gawk}.) - -Some operating systems do not have environment variables. -The array @code{ENVIRON} is empty when running on these systems. - -@item ERRNO -The system error message when an error occurs using @code{getline} -or @code{close}. - -@item FILENAME -The name of the current input file. If no files are specified on the command -line, the value of @code{FILENAME} is @samp{-}. - -@item FNR -The input record number in the current input file. - -@item FS -The input field separator, a blank by default. - -@item IGNORECASE -The case-sensitivity flag for regular expression operations. If -@code{IGNORECASE} has a nonzero value, then pattern matching in rules, -field splitting with @code{FS}, regular expression matching with -@samp{~} and @samp{!~}, and the @code{gsub}, @code{index}, @code{match}, -@code{split} and @code{sub} predefined functions all ignore case -when doing regular expression operations.@refill - -@item NF -The number of fields in the current input record. - -@item NR -The total number of input records seen so far. - -@item OFMT -The output format for numbers for the @code{print} statement, -@code{"%.6g"} by default. - -@item OFS -The output field separator, a blank by default. - -@item ORS -The output record separator, by default a newline. - -@item RS -The input record separator, by default a newline. @code{RS} is exceptional -in that only the first character of its string value is used for separating -records. If @code{RS} is set to the null string, then records are separated by -blank lines. When @code{RS} is set to the null string, then the newline -character always acts as a field separator, in addition to whatever value -@code{FS} may have.@refill - -@item RSTART -The index of the first character matched by @code{match}; 0 if no match. - -@item RLENGTH -The length of the string matched by @code{match}; @minus{}1 if no match. - -@item SUBSEP -The string used to separate multiple subscripts in array elements, by -default @code{"\034"}. -@end table - -@xref{Built-in Variables}, for more information. - -@node Arrays Summary, Data Type Summary, Built-in Summary, Variables/Fields -@appendixsubsec Arrays - -Arrays are subscripted with an expression between square brackets -(@samp{[} and @samp{]}). Array subscripts are @emph{always} strings; -numbers are converted to strings as necessary, following the standard -conversion rules -(@pxref{Conversion, ,Conversion of Strings and Numbers}).@refill - -If you use multiple expressions separated by commas inside the square -brackets, then the array subscript is a string consisting of the -concatenation of the individual subscript values, converted to strings, -separated by the subscript separator (the value of @code{SUBSEP}). - -The special operator @code{in} may be used in an @code{if} or -@code{while} statement to see if an array has an index consisting of a -particular value. - -@example -if (val in array) - print array[val] -@end example - -If the array has multiple subscripts, use @code{(i, j, @dots{}) in array} -to test for existence of an element. - -The @code{in} construct may also be used in a @code{for} loop to iterate -over all the elements of an array. -@xref{Scanning an Array, ,Scanning all Elements of an Array}.@refill - -An element may be deleted from an array using the @code{delete} statement. - -@xref{Arrays, ,Arrays in @code{awk}}, for more detailed information. - -@node Data Type Summary, , Arrays Summary, Variables/Fields -@appendixsubsec Data Types - -The value of an @code{awk} expression is always either a number -or a string. - -Certain contexts (such as arithmetic operators) require numeric -values. They convert strings to numbers by interpreting the text -of the string as a numeral. If the string does not look like a -numeral, it converts to 0. - -Certain contexts (such as concatenation) require string values. -They convert numbers to strings by effectively printing them -with @code{sprintf}. -@xref{Conversion, ,Conversion of Strings and Numbers}, for the details.@refill - -To force conversion of a string value to a number, simply add 0 -to it. If the value you start with is already a number, this -does not change it. - -To force conversion of a numeric value to a string, concatenate it with -the null string. - -The @code{awk} language defines comparisons as being done numerically if -both operands are numeric, or if one is numeric and the other is a numeric -string. Otherwise one or both operands are converted to strings and a -string comparison is performed. - -Uninitialized variables have the string value @code{""} (the null, or -empty, string). In contexts where a number is required, this is -equivalent to 0. - -@xref{Variables}, for more information on variable naming and initialization; -@pxref{Conversion, ,Conversion of Strings and Numbers}, for more information -on how variable values are interpreted.@refill - -@node Rules Summary, Functions Summary, Variables/Fields, Gawk Summary -@appendixsec Patterns and Actions - -@menu -* Pattern Summary:: Quick overview of patterns. -* Regexp Summary:: Quick overview of regular expressions. -* Actions Summary:: Quick overview of actions. -@end menu - -An @code{awk} program is mostly composed of rules, each consisting of a -pattern followed by an action. The action is enclosed in @samp{@{} and -@samp{@}}. Either the pattern may be missing, or the action may be -missing, but, of course, not both. If the pattern is missing, the -action is executed for every single line of input. A missing action is -equivalent to this action, - -@example -@{ print @} -@end example - -@noindent -which prints the entire line. - -Comments begin with the @samp{#} character, and continue until the end of the -line. Blank lines may be used to separate statements. Normally, a statement -ends with a newline, however, this is not the case for lines ending in a -@samp{,}, @samp{@{}, @samp{?}, @samp{:}, @samp{&&}, or @samp{||}. Lines -ending in @code{do} or @code{else} also have their statements automatically -continued on the following line. In other cases, a line can be continued by -ending it with a @samp{\}, in which case the newline is ignored.@refill - -Multiple statements may be put on one line by separating them with a @samp{;}. -This applies to both the statements within the action part of a rule (the -usual case), and to the rule statements. - -@xref{Comments, ,Comments in @code{awk} Programs}, for information on -@code{awk}'s commenting convention; -@pxref{Statements/Lines, ,@code{awk} Statements versus Lines}, for a -description of the line continuation mechanism in @code{awk}.@refill - -@node Pattern Summary, Regexp Summary, Rules Summary, Rules Summary -@appendixsubsec Patterns - -@code{awk} patterns may be one of the following: - -@example -/@var{regular expression}/ -@var{relational expression} -@var{pattern} && @var{pattern} -@var{pattern} || @var{pattern} -@var{pattern} ? @var{pattern} : @var{pattern} -(@var{pattern}) -! @var{pattern} -@var{pattern1}, @var{pattern2} -BEGIN -END -@end example - -@code{BEGIN} and @code{END} are two special kinds of patterns that are not -tested against the input. The action parts of all @code{BEGIN} rules are -merged as if all the statements had been written in a single @code{BEGIN} -rule. They are executed before any of the input is read. Similarly, all the -@code{END} rules are merged, and executed when all the input is exhausted (or -when an @code{exit} statement is executed). @code{BEGIN} and @code{END} -patterns cannot be combined with other patterns in pattern expressions. -@code{BEGIN} and @code{END} rules cannot have missing action parts.@refill - -For @samp{/@var{regular-expression}/} patterns, the associated statement is -executed for each input line that matches the regular expression. Regular -expressions are extensions of those in @code{egrep}, and are summarized below. - -A @var{relational expression} may use any of the operators defined below in -the section on actions. These generally test whether certain fields match -certain regular expressions. - -The @samp{&&}, @samp{||}, and @samp{!} operators are logical ``and,'' -logical ``or,'' and logical ``not,'' respectively, as in C. They do -short-circuit evaluation, also as in C, and are used for combining more -primitive pattern expressions. As in most languages, parentheses may be -used to change the order of evaluation. - -The @samp{?:} operator is like the same operator in C. If the first -pattern matches, then the second pattern is matched against the input -record; otherwise, the third is matched. Only one of the second and -third patterns is matched. - -The @samp{@var{pattern1}, @var{pattern2}} form of a pattern is called a -range pattern. It matches all input lines starting with a line that -matches @var{pattern1}, and continuing until a line that matches -@var{pattern2}, inclusive. A range pattern cannot be used as an operand -to any of the pattern operators. - -@xref{Patterns}, for a full description of the pattern part of @code{awk} -rules. - -@node Regexp Summary, Actions Summary, Pattern Summary, Rules Summary -@appendixsubsec Regular Expressions - -Regular expressions are the extended kind found in @code{egrep}. -They are composed of characters as follows: - -@table @code -@item @var{c} -matches the character @var{c} (assuming @var{c} is a character with no -special meaning in regexps). - -@item \@var{c} -matches the literal character @var{c}. - -@item . -matches any character except newline. - -@item ^ -matches the beginning of a line or a string. - -@item $ -matches the end of a line or a string. - -@item [@var{abc}@dots{}] -matches any of the characters @var{abc}@dots{} (character class). - -@item [^@var{abc}@dots{}] -matches any character except @var{abc}@dots{} and newline (negated -character class). - -@item @var{r1}|@var{r2} -matches either @var{r1} or @var{r2} (alternation). - -@item @var{r1r2} -matches @var{r1}, and then @var{r2} (concatenation). - -@item @var{r}+ -matches one or more @var{r}'s. - -@item @var{r}* -matches zero or more @var{r}'s. - -@item @var{r}? -matches zero or one @var{r}'s. - -@item (@var{r}) -matches @var{r} (grouping). -@end table - -@xref{Regexp, ,Regular Expressions as Patterns}, for a more detailed -explanation of regular expressions. - -The escape sequences allowed in string constants are also valid in -regular expressions (@pxref{Constants, ,Constant Expressions}). - -@node Actions Summary, , Regexp Summary, Rules Summary -@appendixsubsec Actions - -Action statements are enclosed in braces, @samp{@{} and @samp{@}}. -Action statements consist of the usual assignment, conditional, and looping -statements found in most languages. The operators, control statements, -and input/output statements available are patterned after those in C. - -@menu -* Operator Summary:: @code{awk} operators. -* Control Flow Summary:: The control statements. -* I/O Summary:: The I/O statements. -* Printf Summary:: A summary of @code{printf}. -* Special File Summary:: Special file names interpreted internally. -* Numeric Functions Summary:: Built-in numeric functions. -* String Functions Summary:: Built-in string functions. -* Time Functions Summary:: Built-in time functions. -* String Constants Summary:: Escape sequences in strings. -@end menu - -@node Operator Summary, Control Flow Summary, Actions Summary, Actions Summary -@appendixsubsubsec Operators - -The operators in @code{awk}, in order of increasing precedence, are: - -@table @code -@item = += -= *= /= %= ^= -Assignment. Both absolute assignment (@code{@var{var}=@var{value}}) -and operator assignment (the other forms) are supported. - -@item ?: -A conditional expression, as in C. This has the form @code{@var{expr1} ? -@var{expr2} : @var{expr3}}. If @var{expr1} is true, the value of the -expression is @var{expr2}; otherwise it is @var{expr3}. Only one of -@var{expr2} and @var{expr3} is evaluated.@refill - -@item || -Logical ``or''. - -@item && -Logical ``and''. - -@item ~ !~ -Regular expression match, negated match. - -@item < <= > >= != == -The usual relational operators. - -@item @var{blank} -String concatenation. - -@item + - -Addition and subtraction. - -@item * / % -Multiplication, division, and modulus. - -@item + - ! -Unary plus, unary minus, and logical negation. - -@item ^ -Exponentiation (@samp{**} may also be used, and @samp{**=} for the assignment -operator, but they are not specified in the @sc{posix} standard). - -@item ++ -- -Increment and decrement, both prefix and postfix. - -@item $ -Field reference. -@end table - -@xref{Expressions, ,Expressions as Action Statements}, for a full -description of all the operators listed above. -@xref{Fields, ,Examining Fields}, for a description of the field -reference operator.@refill - -@node Control Flow Summary, I/O Summary, Operator Summary, Actions Summary -@appendixsubsubsec Control Statements - -The control statements are as follows: - -@example -if (@var{condition}) @var{statement} @r{[} else @var{statement} @r{]} -while (@var{condition}) @var{statement} -do @var{statement} while (@var{condition}) -for (@var{expr1}; @var{expr2}; @var{expr3}) @var{statement} -for (@var{var} in @var{array}) @var{statement} -break -continue -delete @var{array}[@var{index}] -exit @r{[} @var{expression} @r{]} -@{ @var{statements} @} -@end example - -@xref{Statements, ,Control Statements in Actions}, for a full description -of all the control statements listed above. - -@node I/O Summary, Printf Summary, Control Flow Summary, Actions Summary -@appendixsubsubsec I/O Statements - -The input/output statements are as follows: - -@table @code -@item getline -Set @code{$0} from next input record; set @code{NF}, @code{NR}, @code{FNR}. - -@item getline <@var{file} -Set @code{$0} from next record of @var{file}; set @code{NF}. - -@item getline @var{var} -Set @var{var} from next input record; set @code{NF}, @code{FNR}. - -@item getline @var{var} <@var{file} -Set @var{var} from next record of @var{file}. - -@item next -Stop processing the current input record. The next input record is read and -processing starts over with the first pattern in the @code{awk} program. -If the end of the input data is reached, the @code{END} rule(s), if any, -are executed. - -@item next file -Stop processing the current input file. The next input record read comes -from the next input file. @code{FILENAME} is updated, @code{FNR} is set to 1, -and processing starts over with the first pattern in the @code{awk} program. -If the end of the input data is reached, the @code{END} rule(s), if any, -are executed. - -@item print -Prints the current record. - -@item print @var{expr-list} -Prints expressions. - -@item print @var{expr-list} > @var{file} -Prints expressions on @var{file}. - -@item printf @var{fmt, expr-list} -Format and print. - -@item printf @var{fmt, expr-list} > file -Format and print on @var{file}. -@end table - -Other input/output redirections are also allowed. For @code{print} and -@code{printf}, @samp{>> @var{file}} appends output to the @var{file}, -and @samp{| @var{command}} writes on a pipe. In a similar fashion, -@samp{@var{command} | getline} pipes input into @code{getline}. -@code{getline} returns 0 on end of file, and @minus{}1 on an error.@refill - -@xref{Getline, ,Explicit Input with @code{getline}}, for a full description -of the @code{getline} statement. -@xref{Printing, ,Printing Output}, for a full description of @code{print} and -@code{printf}. Finally, @pxref{Next Statement, ,The @code{next} Statement}, -for a description of how the @code{next} statement works.@refill - -@node Printf Summary, Special File Summary, I/O Summary, Actions Summary -@appendixsubsubsec @code{printf} Summary - -The @code{awk} @code{printf} statement and @code{sprintf} function -accept the following conversion specification formats: - -@table @code -@item %c -An ASCII character. If the argument used for @samp{%c} is numeric, it is -treated as a character and printed. Otherwise, the argument is assumed to -be a string, and the only first character of that string is printed. - -@item %d -@itemx %i -A decimal number (the integer part). - -@item %e -A floating point number of the form -@samp{@r{[}-@r{]}d.ddddddE@r{[}+-@r{]}dd}.@refill - -@item %f -A floating point number of the form -@r{[}@code{-}@r{]}@code{ddd.dddddd}. - -@item %g -Use @samp{%e} or @samp{%f} conversion, whichever produces a shorter string, -with nonsignificant zeros suppressed. - -@item %o -An unsigned octal number (again, an integer). - -@item %s -A character string. - -@item %x -An unsigned hexadecimal number (an integer). - -@item %X -Like @samp{%x}, except use @samp{A} through @samp{F} instead of @samp{a} -through @samp{f} for decimal 10 through 15.@refill - -@item %% -A single @samp{%} character; no argument is converted. -@end table - -There are optional, additional parameters that may lie between the @samp{%} -and the control letter: - -@table @code -@item - -The expression should be left-justified within its field. - -@item @var{width} -The field should be padded to this width. If @var{width} has a leading zero, -then the field is padded with zeros. Otherwise it is padded with blanks. - -@item .@var{prec} -A number indicating the maximum width of strings or digits to the right -of the decimal point. -@end table - -Either or both of the @var{width} and @var{prec} values may be specified -as @samp{*}. In that case, the particular value is taken from the argument -list. - -@xref{Printf, ,Using @code{printf} Statements for Fancier Printing}, for -examples and for a more detailed description. - -@node Special File Summary, Numeric Functions Summary, Printf Summary, Actions Summary -@appendixsubsubsec Special File Names - -When doing I/O redirection from either @code{print} or @code{printf} into a -file, or via @code{getline} from a file, @code{gawk} recognizes certain special -file names internally. These file names allow access to open file descriptors -inherited from @code{gawk}'s parent process (usually the shell). The -file names are: - -@table @file -@item /dev/stdin -The standard input. - -@item /dev/stdout -The standard output. - -@item /dev/stderr -The standard error output. - -@item /dev/fd/@var{n} -The file denoted by the open file descriptor @var{n}. -@end table - -In addition the following files provide process related information -about the running @code{gawk} program. - -@table @file -@item /dev/pid -Reading this file returns the process ID of the current process, -in decimal, terminated with a newline. - -@item /dev/ppid -Reading this file returns the parent process ID of the current process, -in decimal, terminated with a newline. - -@item /dev/pgrpid -Reading this file returns the process group ID of the current process, -in decimal, terminated with a newline. - -@item /dev/user -Reading this file returns a single record terminated with a newline. -The fields are separated with blanks. The fields represent the -following information: - -@table @code -@item $1 -The value of the @code{getuid} system call. - -@item $2 -The value of the @code{geteuid} system call. - -@item $3 -The value of the @code{getgid} system call. - -@item $4 -The value of the @code{getegid} system call. -@end table - -If there are any additional fields, they are the group IDs returned by -@code{getgroups} system call. -(Multiple groups may not be supported on all systems.)@refill -@end table - -@noindent -These file names may also be used on the command line to name data files. -These file names are only recognized internally if you do not -actually have files by these names on your system. - -@xref{Special Files, ,Standard I/O Streams}, for a longer description that -provides the motivation for this feature. - -@node Numeric Functions Summary, String Functions Summary, Special File Summary, Actions Summary -@appendixsubsubsec Numeric Functions - -@code{awk} has the following predefined arithmetic functions: - -@table @code -@item atan2(@var{y}, @var{x}) -returns the arctangent of @var{y/x} in radians. - -@item cos(@var{expr}) -returns the cosine in radians. - -@item exp(@var{expr}) -the exponential function. - -@item int(@var{expr}) -truncates to integer. - -@item log(@var{expr}) -the natural logarithm function. - -@item rand() -returns a random number between 0 and 1. - -@item sin(@var{expr}) -returns the sine in radians. - -@item sqrt(@var{expr}) -the square root function. - -@item srand(@var{expr}) -use @var{expr} as a new seed for the random number generator. If no @var{expr} -is provided, the time of day is used. The return value is the previous -seed for the random number generator. -@end table - -@node String Functions Summary, Time Functions Summary, Numeric Functions Summary, Actions Summary -@appendixsubsubsec String Functions - -@code{awk} has the following predefined string functions: - -@table @code -@item gsub(@var{r}, @var{s}, @var{t}) -for each substring matching the regular expression @var{r} in the string -@var{t}, substitute the string @var{s}, and return the number of substitutions. -If @var{t} is not supplied, use @code{$0}. - -@item index(@var{s}, @var{t}) -returns the index of the string @var{t} in the string @var{s}, or 0 if -@var{t} is not present. - -@item length(@var{s}) -returns the length of the string @var{s}. The length of @code{$0} -is returned if no argument is supplied. - -@item match(@var{s}, @var{r}) -returns the position in @var{s} where the regular expression @var{r} -occurs, or 0 if @var{r} is not present, and sets the values of @code{RSTART} -and @code{RLENGTH}. - -@item split(@var{s}, @var{a}, @var{r}) -splits the string @var{s} into the array @var{a} on the regular expression -@var{r}, and returns the number of fields. If @var{r} is omitted, @code{FS} -is used instead. - -@item sprintf(@var{fmt}, @var{expr-list}) -prints @var{expr-list} according to @var{fmt}, and returns the resulting string. - -@item sub(@var{r}, @var{s}, @var{t}) -this is just like @code{gsub}, but only the first matching substring is -replaced. - -@item substr(@var{s}, @var{i}, @var{n}) -returns the @var{n}-character substring of @var{s} starting at @var{i}. -If @var{n} is omitted, the rest of @var{s} is used. - -@item tolower(@var{str}) -returns a copy of the string @var{str}, with all the upper-case characters in -@var{str} translated to their corresponding lower-case counterparts. -Nonalphabetic characters are left unchanged. - -@item toupper(@var{str}) -returns a copy of the string @var{str}, with all the lower-case characters in -@var{str} translated to their corresponding upper-case counterparts. -Nonalphabetic characters are left unchanged. - -@item system(@var{cmd-line}) -Execute the command @var{cmd-line}, and return the exit status. -@end table - -@node Time Functions Summary, String Constants Summary, String Functions Summary, Actions Summary -@appendixsubsubsec Built-in time functions - -The following two functions are available for getting the current -time of day, and for formatting time stamps. - -@table @code -@item systime() -returns the current time of day as the number of seconds since a particular -epoch (Midnight, January 1, 1970 @sc{utc}, on @sc{posix} systems). - -@item strftime(@var{format}, @var{timestamp}) -formats @var{timestamp} according to the specification in @var{format}. -The current time of day is used if no @var{timestamp} is supplied. -@xref{Time Functions, ,Functions for Dealing with Time Stamps}, for the -details on the conversion specifiers that @code{strftime} accepts.@refill -@end table - -@iftex -@xref{Built-in, ,Built-in Functions}, for a description of all of -@code{awk}'s built-in functions. -@end iftex - -@node String Constants Summary, , Time Functions Summary, Actions Summary -@appendixsubsubsec String Constants - -String constants in @code{awk} are sequences of characters enclosed -between double quotes (@code{"}). Within strings, certain @dfn{escape sequences} -are recognized, as in C. These are: - -@table @code -@item \\ -A literal backslash. - -@item \a -The ``alert'' character; usually the ASCII BEL character. - -@item \b -Backspace. - -@item \f -Formfeed. - -@item \n -Newline. - -@item \r -Carriage return. - -@item \t -Horizontal tab. - -@item \v -Vertical tab. - -@item \x@var{hex digits} -The character represented by the string of hexadecimal digits following -the @samp{\x}. As in @sc{ansi} C, all following hexadecimal digits are -considered part of the escape sequence. (This feature should tell us -something about language design by committee.) E.g., @code{"\x1B"} is a -string containing the ASCII ESC (escape) character. (The @samp{\x} -escape sequence is not in @sc{posix} @code{awk}.) - -@item \@var{ddd} -The character represented by the 1-, 2-, or 3-digit sequence of octal -digits. Thus, @code{"\033"} is also a string containing the ASCII ESC -(escape) character. - -@item \@var{c} -The literal character @var{c}. -@end table - -The escape sequences may also be used inside constant regular expressions -(e.g., the regexp @code{@w{/[@ \t\f\n\r\v]/}} matches whitespace -characters).@refill - -@xref{Constants, ,Constant Expressions}. - -@node Functions Summary, Historical Features, Rules Summary, Gawk Summary -@appendixsec Functions - -Functions in @code{awk} are defined as follows: - -@example -function @var{name}(@var{parameter list}) @{ @var{statements} @} -@end example - -Actual parameters supplied in the function call are used to instantiate -the formal parameters declared in the function. Arrays are passed by -reference, other variables are passed by value. - -If there are fewer arguments passed than there are names in @var{parameter-list}, -the extra names are given the null string as value. Extra names have the -effect of local variables. - -The open-parenthesis in a function call of a user-defined function must -immediately follow the function name, without any intervening white space. -This is to avoid a syntactic ambiguity with the concatenation operator. - -The word @code{func} may be used in place of @code{function} (but not in -@sc{posix} @code{awk}). - -Use the @code{return} statement to return a value from a function. - -@xref{User-defined, ,User-defined Functions}, for a more complete description. - -@node Historical Features, , Functions Summary, Gawk Summary -@appendixsec Historical Features - -There are two features of historical @code{awk} implementations that -@code{gawk} supports. First, it is possible to call the @code{length} -built-in function not only with no arguments, but even without parentheses! - -@example -a = length -@end example - -@noindent -is the same as either of - -@example -a = length() -a = length($0) -@end example - -@noindent -This feature is marked as ``deprecated'' in the @sc{posix} standard, and -@code{gawk} will issue a warning about its use if @samp{-W lint} is -specified on the command line. - -The other feature is the use of the @code{continue} statement outside the -body of a @code{while}, @code{for}, or @code{do} loop. Traditional -@code{awk} implementations have treated such usage as equivalent to the -@code{next} statement. @code{gawk} will support this usage if @samp{-W posix} -has not been specified. - -@node Sample Program, Bugs, Gawk Summary, Top -@appendix Sample Program - -The following example is a complete @code{awk} program, which prints -the number of occurrences of each word in its input. It illustrates the -associative nature of @code{awk} arrays by using strings as subscripts. It -also demonstrates the @samp{for @var{x} in @var{array}} construction. -Finally, it shows how @code{awk} can be used in conjunction with other -utility programs to do a useful task of some complexity with a minimum of -effort. Some explanations follow the program listing.@refill - -@example -awk ' -# Print list of word frequencies -@{ - for (i = 1; i <= NF; i++) - freq[$i]++ -@} - -END @{ - for (word in freq) - printf "%s\t%d\n", word, freq[word] -@}' -@end example - -The first thing to notice about this program is that it has two rules. The -first rule, because it has an empty pattern, is executed on every line of -the input. It uses @code{awk}'s field-accessing mechanism -(@pxref{Fields, ,Examining Fields}) to pick out the individual words from -the line, and the built-in variable @code{NF} (@pxref{Built-in Variables}) -to know how many fields are available.@refill - -For each input word, an element of the array @code{freq} is incremented to -reflect that the word has been seen an additional time.@refill - -The second rule, because it has the pattern @code{END}, is not executed -until the input has been exhausted. It prints out the contents of the -@code{freq} table that has been built up inside the first action.@refill - -Note that this program has several problems that would prevent it from being -useful by itself on real text files:@refill - -@itemize @bullet -@item -Words are detected using the @code{awk} convention that fields are -separated by whitespace and that other characters in the input (except -newlines) don't have any special meaning to @code{awk}. This means that -punctuation characters count as part of words.@refill - -@item -The @code{awk} language considers upper and lower case characters to be -distinct. Therefore, @samp{foo} and @samp{Foo} are not treated by this -program as the same word. This is undesirable since in normal text, words -are capitalized if they begin sentences, and a frequency analyzer should not -be sensitive to that.@refill - -@item -The output does not come out in any useful order. You're more likely to be -interested in which words occur most frequently, or having an alphabetized -table of how frequently each word occurs.@refill -@end itemize - -The way to solve these problems is to use some of the more advanced -features of the @code{awk} language. First, we use @code{tolower} to remove -case distinctions. Next, we use @code{gsub} to remove punctuation -characters. Finally, we use the system @code{sort} utility to process the -output of the @code{awk} script. First, here is the new version of -the program:@refill - -@example -awk ' -# Print list of word frequencies -@{ - $0 = tolower($0) # remove case distinctions - gsub(/[^a-z0-9_ \t]/, "", $0) # remove punctuation - for (i = 1; i <= NF; i++) - freq[$i]++ -@} - -END @{ - for (word in freq) - printf "%s\t%d\n", word, freq[word] -@}' -@end example - -Assuming we have saved this program in a file named @file{frequency.awk}, -and that the data is in @file{file1}, the following pipeline - -@example -awk -f frequency.awk file1 | sort +1 -nr -@end example - -@noindent -produces a table of the words appearing in @file{file1} in order of -decreasing frequency. - -The @code{awk} program suitably massages the data and produces a word -frequency table, which is not ordered. - -The @code{awk} script's output is then sorted by the @code{sort} command and -printed on the terminal. The options given to @code{sort} in this example -specify to sort using the second field of each input line (skipping one field), -that the sort keys should be treated as numeric quantities (otherwise -@samp{15} would come before @samp{5}), and that the sorting should be done -in descending (reverse) order.@refill - -We could have even done the @code{sort} from within the program, by -changing the @code{END} action to: - -@example -END @{ - sort = "sort +1 -nr" - for (word in freq) - printf "%s\t%d\n", word, freq[word] | sort - close(sort) -@}' -@end example - -See the general operating system documentation for more information on how -to use the @code{sort} command.@refill - -@ignore -@strong{ADR: I have some more substantial programs courtesy of Rick Adams -at UUNET. I am planning on incorporating those either in addition to or -instead of this program.} - -@strong{I would also like to incorporate the general @code{translate} -function that I have written.} - -@strong{I have a ton of other sample programs to include too.} -@end ignore - -@node Bugs, Notes, Sample Program, Top -@appendix Reporting Problems and Bugs - -@c This chapter stolen shamelessly from the GNU m4 manual. -@c This chapter has been unshamelessly altered to emulate changes made to -@c make.texi from whence it was originally shamelessly stolen! :-} --mew - -If you have problems with @code{gawk} or think that you have found a bug, -please report it to the developers; we cannot promise to do anything -but we might well want to fix it. - -Before reporting a bug, make sure you have actually found a real bug. -Carefully reread the documentation and see if it really says you can do -what you're trying to do. If it's not clear whether you should be able -to do something or not, report that too; it's a bug in the documentation! - -Before reporting a bug or trying to fix it yourself, try to isolate it -to the smallest possible @code{awk} program and input data file that -reproduces the problem. Then send us the program and data file, -some idea of what kind of Unix system you're using, and the exact results -@code{gawk} gave you. Also say what you expected to occur; this will help -us decide whether the problem was really in the documentation. - -Once you have a precise problem, send e-mail to (Internet) -@samp{bug-gnu-utils@@prep.ai.mit.edu} or (UUCP) -@samp{mit-eddie!prep.ai.mit.edu!bug-gnu-utils}. Please include the -version number of @code{gawk} you are using. You can get this information -with the command @samp{gawk -W version '@{@}' /dev/null}. -You should send carbon copies of your mail to David Trueman at -@samp{david@@cs.dal.ca}, and to Arnold Robbins, who can be reached at -@samp{arnold@@skeeve.atl.ga.us}. David is most likely to fix code -problems, while Arnold is most likely to fix documentation problems.@refill - -Non-bug suggestions are always welcome as well. If you have questions -about things that are unclear in the documentation or are just obscure -features, ask Arnold Robbins; he will try to help you out, although he -may not have the time to fix the problem. You can send him electronic mail at the Internet address -above. - -If you find bugs in one of the non-Unix ports of @code{gawk}, please send -an electronic mail message to the person who maintains that port. They -are listed below, and also in the @file{README} file in the @code{gawk} -distribution. Information in the @code{README} file should be considered -authoritative if it conflicts with this manual. - -The people maintaining the non-Unix ports of @code{gawk} are: - -@table @asis -@item MS-DOS -The port to MS-DOS is maintained by Scott Deifik. -His electronic mail address is @samp{scottd@@amgen.com}. - -@item VMS -The port to VAX VMS is maintained by Pat Rankin. -His electronic mail address is @samp{rankin@@eql.caltech.edu}. - -@item Atari ST -The port to the Atari ST is maintained by Michal Jaegermann. -His electronic mail address is @samp{ntomczak@@vm.ucs.ualberta.ca}. - -@end table - -If your bug is also reproducible under Unix, please send copies of your -report to the general GNU bug list, as well as to Arnold Robbins and David -Trueman, at the addresses listed above. - -@node Notes, Glossary, Bugs, Top -@appendix Implementation Notes - -This appendix contains information mainly of interest to implementors and -maintainers of @code{gawk}. Everything in it applies specifically to -@code{gawk}, and not to other implementations. - -@menu -* Compatibility Mode:: How to disable certain @code{gawk} extensions. -* Future Extensions:: New features we may implement soon. -* Improvements:: Suggestions for improvements by volunteers. -@end menu - -@node Compatibility Mode, Future Extensions, Notes, Notes -@appendixsec Downward Compatibility and Debugging - -@xref{POSIX/GNU, ,Extensions in @code{gawk} not in POSIX @code{awk}}, -for a summary of the GNU extensions to the @code{awk} language and program. -All of these features can be turned off by invoking @code{gawk} with the -@samp{-W compat} option, or with the @samp{-W posix} option.@refill - -If @code{gawk} is compiled for debugging with @samp{-DDEBUG}, then there -is one more option available on the command line: - -@table @samp -@item -W parsedebug -Print out the parse stack information as the program is being parsed. -@end table - -This option is intended only for serious @code{gawk} developers, -and not for the casual user. It probably has not even been compiled into -your version of @code{gawk}, since it slows down execution. - -@node Future Extensions, Improvements, Compatibility Mode, Notes -@appendixsec Probable Future Extensions - -This section briefly lists extensions that indicate the directions we are -currently considering for @code{gawk}. The file @file{FUTURES} in the -@code{gawk} distributions lists these extensions, as well as several others. - -@table @asis -@item @code{RS} as a regexp -The meaning of @code{RS} may be generalized along the lines of @code{FS}. - -@item Control of subprocess environment -Changes made in @code{gawk} to the array @code{ENVIRON} may be -propagated to subprocesses run by @code{gawk}. - -@item Databases -It may be possible to map a GDBM/NDBM/SDBM file into an @code{awk} array. - -@item Single-character fields -The null string, @code{""}, as a field separator, will cause field -splitting and the @code{split} function to separate individual characters. -Thus, @code{split(a, "abcd", "")} would yield @code{a[1] == "a"}, -@code{a[2] == "b"}, and so on. - -@item More @code{lint} warnings -There are more things that could be checked for portability. - -@item @code{RECLEN} variable for fixed length records -Along with @code{FIELDWIDTHS}, this would speed up the processing of -fixed-length records. - -@item @code{RT} variable to hold the record terminator -It is occasionally useful to have access to the actual string of -characters that matched the @code{RS} variable. The @code{RT} -variable would hold these characters. - -@item A @code{restart} keyword -After modifying @code{$0}, @code{restart} would restart the pattern -matching loop, without reading a new record from the input. - -@item A @samp{|&} redirection -The @samp{|&} redirection, in place of @samp{|}, would open a two-way -pipeline for communication with a sub-process (via @code{getline} and -@code{print} and @code{printf}). - -@item @code{IGNORECASE} affecting all comparisons -The effects of the @code{IGNORECASE} variable may be generalized to -all string comparisons, and not just regular expression operations. - -@item A way to mix command line source code and library files -There may be a new option that would make it possible to easily use library -functions from a program entered on the command line. -@c probably a @samp{-s} option... - -@item GNU-style long options -We will add GNU-style long options -to @code{gawk} for compatibility with other GNU programs. -(For example, @samp{--field-separator=:} would be equivalent to -@samp{-F:}.)@refill - -@c this is @emph{very} long term --- not worth including right now. -@ignore -@item The C Comma Operator -We may add the C comma operator, which takes the form -@code{@var{expr1},@var{expr2}}. The first expression is evaluated, and the -result is thrown away. The value of the full expression is the value of -@var{expr2}.@refill -@end ignore -@end table - -@node Improvements, , Future Extensions, Notes -@appendixsec Suggestions for Improvements - -Here are some projects that would-be @code{gawk} hackers might like to take -on. They vary in size from a few days to a few weeks of programming, -depending on which one you choose and how fast a programmer you are. Please -send any improvements you write to the maintainers at the GNU -project.@refill - -@enumerate -@item -Compilation of @code{awk} programs: @code{gawk} uses a Bison (YACC-like) -parser to convert the script given it into a syntax tree; the syntax -tree is then executed by a simple recursive evaluator. This method incurs -a lot of overhead, since the recursive evaluator performs many procedure -calls to do even the simplest things.@refill - -It should be possible for @code{gawk} to convert the script's parse tree -into a C program which the user would then compile, using the normal -C compiler and a special @code{gawk} library to provide all the needed -functions (regexps, fields, associative arrays, type coercion, and so -on).@refill - -An easier possibility might be for an intermediate phase of @code{awk} to -convert the parse tree into a linear byte code form like the one used -in GNU Emacs Lisp. The recursive evaluator would then be replaced by -a straight line byte code interpreter that would be intermediate in speed -between running a compiled program and doing what @code{gawk} does -now.@refill - -This may actually happen for the 3.0 version of @code{gawk}. - -@item -An error message section has not been included in this version of the -manual. Perhaps some nice beta testers will document some of the messages -for the future. - -@item -The programs in the test suite could use documenting in this manual. - -@item -The programs and data files in the manual should be available in -separate files to facilitate experimentation. - -@item -See the @file{FUTURES} file for more ideas. Contact us if you would -seriously like to tackle any of the items listed there. -@end enumerate - -@node Glossary, Index, Notes, Top -@appendix Glossary - -@table @asis -@item Action -A series of @code{awk} statements attached to a rule. If the rule's -pattern matches an input record, the @code{awk} language executes the -rule's action. Actions are always enclosed in curly braces. -@xref{Actions, ,Overview of Actions}.@refill - -@item Amazing @code{awk} Assembler -Henry Spencer at the University of Toronto wrote a retargetable assembler -completely as @code{awk} scripts. It is thousands of lines long, including -machine descriptions for several 8-bit microcomputers. -@c It is distributed with @code{gawk} (as part of the test suite) and -It is a good example of a -program that would have been better written in another language.@refill - -@item @sc{ansi} -The American National Standards Institute. This organization produces -many standards, among them the standard for the C programming language. - -@item Assignment -An @code{awk} expression that changes the value of some @code{awk} -variable or data object. An object that you can assign to is called an -@dfn{lvalue}. @xref{Assignment Ops, ,Assignment Expressions}.@refill - -@item @code{awk} Language -The language in which @code{awk} programs are written. - -@item @code{awk} Program -An @code{awk} program consists of a series of @dfn{patterns} and -@dfn{actions}, collectively known as @dfn{rules}. For each input record -given to the program, the program's rules are all processed in turn. -@code{awk} programs may also contain function definitions.@refill - -@item @code{awk} Script -Another name for an @code{awk} program. - -@item Built-in Function -The @code{awk} language provides built-in functions that perform various -numerical, time stamp related, and string computations. Examples are -@code{sqrt} (for the square root of a number) and @code{substr} (for a -substring of a string). @xref{Built-in, ,Built-in Functions}.@refill - -@item Built-in Variable -@code{ARGC}, @code{ARGIND}, @code{ARGV}, @code{CONVFMT}, @code{ENVIRON}, -@code{ERRNO}, @code{FIELDWIDTHS}, @code{FILENAME}, @code{FNR}, @code{FS}, -@code{IGNORECASE}, @code{NF}, @code{NR}, @code{OFMT}, @code{OFS}, @code{ORS}, -@code{RLENGTH}, @code{RSTART}, @code{RS}, and @code{SUBSEP}, -are the variables that have special -meaning to @code{awk}. Changing some of them affects @code{awk}'s running -environment. @xref{Built-in Variables}.@refill - -@item Braces -See ``Curly Braces.'' - -@item C -The system programming language that most GNU software is written in. The -@code{awk} programming language has C-like syntax, and this manual -points out similarities between @code{awk} and C when appropriate.@refill - -@item CHEM -A preprocessor for @code{pic} that reads descriptions of molecules -and produces @code{pic} input for drawing them. It was written by -Brian Kernighan, and is available from @code{netlib@@research.att.com}.@refill - -@item Compound Statement -A series of @code{awk} statements, enclosed in curly braces. Compound -statements may be nested. -@xref{Statements, ,Control Statements in Actions}.@refill - -@item Concatenation -Concatenating two strings means sticking them together, one after another, -giving a new string. For example, the string @samp{foo} concatenated with -the string @samp{bar} gives the string @samp{foobar}. -@xref{Concatenation, ,String Concatenation}.@refill - -@item Conditional Expression -An expression using the @samp{?:} ternary operator, such as -@code{@var{expr1} ? @var{expr2} : @var{expr3}}. The expression -@var{expr1} is evaluated; if the result is true, the value of the whole -expression is the value of @var{expr2} otherwise the value is -@var{expr3}. In either case, only one of @var{expr2} and @var{expr3} -is evaluated. @xref{Conditional Exp, ,Conditional Expressions}.@refill - -@item Constant Regular Expression -A constant regular expression is a regular expression written within -slashes, such as @samp{/foo/}. This regular expression is chosen -when you write the @code{awk} program, and cannot be changed doing -its execution. @xref{Regexp Usage, ,How to Use Regular Expressions}. - -@item Comparison Expression -A relation that is either true or false, such as @code{(a < b)}. -Comparison expressions are used in @code{if}, @code{while}, and @code{for} -statements, and in patterns to select which input records to process. -@xref{Comparison Ops, ,Comparison Expressions}.@refill - -@item Curly Braces -The characters @samp{@{} and @samp{@}}. Curly braces are used in -@code{awk} for delimiting actions, compound statements, and function -bodies.@refill - -@item Data Objects -These are numbers and strings of characters. Numbers are converted into -strings and vice versa, as needed. -@xref{Conversion, ,Conversion of Strings and Numbers}.@refill - -@item Dynamic Regular Expression -A dynamic regular expression is a regular expression written as an -ordinary expression. It could be a string constant, such as -@code{"foo"}, but it may also be an expression whose value may vary. -@xref{Regexp Usage, ,How to Use Regular Expressions}. - -@item Escape Sequences -A special sequence of characters used for describing nonprinting -characters, such as @samp{\n} for newline, or @samp{\033} for the ASCII -ESC (escape) character. @xref{Constants, ,Constant Expressions}. - -@item Field -When @code{awk} reads an input record, it splits the record into pieces -separated by whitespace (or by a separator regexp which you can -change by setting the built-in variable @code{FS}). Such pieces are -called fields. If the pieces are of fixed length, you can use the built-in -variable @code{FIELDWIDTHS} to describe their lengths. -@xref{Records, ,How Input is Split into Records}.@refill - -@item Format -Format strings are used to control the appearance of output in the -@code{printf} statement. Also, data conversions from numbers to strings -are controlled by the format string contained in the built-in variable -@code{CONVFMT}. @xref{Control Letters, ,Format-Control Letters}.@refill - -@item Function -A specialized group of statements often used to encapsulate general -or program-specific tasks. @code{awk} has a number of built-in -functions, and also allows you to define your own. -@xref{Built-in, ,Built-in Functions}. -Also, see @ref{User-defined, ,User-defined Functions}.@refill - -@item @code{gawk} -The GNU implementation of @code{awk}. - -@item GNU -``GNU's not Unix''. An on-going project of the Free Software Foundation -to create a complete, freely distributable, @sc{posix}-compliant computing -environment. - -@item Input Record -A single chunk of data read in by @code{awk}. Usually, an @code{awk} input -record consists of one line of text. -@xref{Records, ,How Input is Split into Records}.@refill - -@item Keyword -In the @code{awk} language, a keyword is a word that has special -meaning. Keywords are reserved and may not be used as variable names. - -@code{awk}'s keywords are: -@code{if}, -@code{else}, -@code{while}, -@code{do@dots{}while}, -@code{for}, -@code{for@dots{}in}, -@code{break}, -@code{continue}, -@code{delete}, -@code{next}, -@code{function}, -@code{func}, -and @code{exit}.@refill - -@item Lvalue -An expression that can appear on the left side of an assignment -operator. In most languages, lvalues can be variables or array -elements. In @code{awk}, a field designator can also be used as an -lvalue.@refill - -@item Number -A numeric valued data object. The @code{gawk} implementation uses double -precision floating point to represent numbers.@refill - -@item Pattern -Patterns tell @code{awk} which input records are interesting to which -rules. - -A pattern is an arbitrary conditional expression against which input is -tested. If the condition is satisfied, the pattern is said to @dfn{match} -the input record. A typical pattern might compare the input record against -a regular expression. @xref{Patterns}.@refill - -@item @sc{posix} -The name for a series of standards being developed by the @sc{ieee} -that specify a Portable Operating System interface. The ``IX'' denotes -the Unix heritage of these standards. The main standard of interest for -@code{awk} users is P1003.2, the Command Language and Utilities standard. - -@item Range (of input lines) -A sequence of consecutive lines from the input file. A pattern -can specify ranges of input lines for @code{awk} to process, or it can -specify single lines. @xref{Patterns}.@refill - -@item Recursion -When a function calls itself, either directly or indirectly. -If this isn't clear, refer to the entry for ``recursion.'' - -@item Redirection -Redirection means performing input from other than the standard input -stream, or output to other than the standard output stream. - -You can redirect the output of the @code{print} and @code{printf} statements -to a file or a system command, using the @samp{>}, @samp{>>}, and @samp{|} -operators. You can redirect input to the @code{getline} statement using -the @samp{<} and @samp{|} operators. -@xref{Redirection, ,Redirecting Output of @code{print} and @code{printf}}.@refill - -@item Regular Expression -See ``regexp.'' - -@item Regexp -Short for @dfn{regular expression}. A regexp is a pattern that denotes a -set of strings, possibly an infinite set. For example, the regexp -@samp{R.*xp} matches any string starting with the letter @samp{R} -and ending with the letters @samp{xp}. In @code{awk}, regexps are -used in patterns and in conditional expressions. Regexps may contain -escape sequences. @xref{Regexp, ,Regular Expressions as Patterns}.@refill - -@item Rule -A segment of an @code{awk} program, that specifies how to process single -input records. A rule consists of a @dfn{pattern} and an @dfn{action}. -@code{awk} reads an input record; then, for each rule, if the input record -satisfies the rule's pattern, @code{awk} executes the rule's action. -Otherwise, the rule does nothing for that input record.@refill - -@item Side Effect -A side effect occurs when an expression has an effect aside from merely -producing a value. Assignment expressions, increment expressions and -function calls have side effects. @xref{Assignment Ops, ,Assignment Expressions}. - -@item Special File -A file name interpreted internally by @code{gawk}, instead of being handed -directly to the underlying operating system. For example, @file{/dev/stdin}. -@xref{Special Files, ,Standard I/O Streams}. - -@item Stream Editor -A program that reads records from an input stream and processes them one -or more at a time. This is in contrast with batch programs, which may -expect to read their input files in entirety before starting to do -anything, and with interactive programs, which require input from the -user.@refill - -@item String -A datum consisting of a sequence of characters, such as @samp{I am a -string}. Constant strings are written with double-quotes in the -@code{awk} language, and may contain escape sequences. -@xref{Constants, ,Constant Expressions}. - -@item Whitespace -A sequence of blank or tab characters occurring inside an input record or a -string.@refill -@end table - -@node Index, , Glossary, Top -@unnumbered Index -@printindex cp - -@summarycontents -@contents -@bye - -Unresolved Issues: ------------------- -1. From: ntomczak@vm.ucs.ualberta.ca (Michal Jaegermann) - Examples of usage tend to suggest that /../ and ".." delimiters - can be used for regular expressions, even if definition is consistently - using /../. I am not sure what the real rules are and in particular - what of the following is a bug and what is a feature: - # This program matches everything - '"\(" { print }' - # This one complains about mismatched parenthesis - '$0 ~ "\(" { print }' - # This one behaves in an expected manner - '/\(/ { print }' - You may also try to use "\(" as an argument to match() to see what - will happen. - -2. From ADR. - - The posix (and original Unix!) notion of awk values as both number - and string values needs to be put into the manual. This involves - major and minor rewrites of most of the manual, but should help in - clarifying many of the weirder points of the language. - -3. From ADR. - - The manual should be reorganized. Expressions should be introduced - early, building up to regexps as expressions, and from there to their - use as patterns and then in actions. Built-in vars should come earlier - in the manual too. The 'expert info' sections marked with comments - should get their own sections or subsections with nodes and titles. - The manual should be gone over thoroughly for indexing. - -4. From ADR. - - Robert J. Chassell points out that awk programs should have some indication - of how to use them. It would be useful to perhaps have a "programming - style" section of the manual that would include this and other tips. - -5. From ADR in response to moraes@uunet.ca - (This would make the beginnings of a good "puzzles" section...) - - Date: Mon, 2 Dec 91 10:08:05 EST - From: gatech!cc!arnold (Arnold Robbins) - To: cs.dal.ca!david, uunet.ca!moraes - Subject: redirecting to /dev/stderr - Cc: skeeve!arnold, boeing.com!brennan, research.att.com!bwk - - In 2.13.3 the following program no longer dumps core: - - BEGIN { print "hello" > /dev/stderr ; exit(1) } - - Instead, it creates a file named `0' with the word `hello' in it. AWK - semantics strikes again. The meaning of the statement is - - print "hello" > (($0 ~ /dev/) stderr) - - /dev/ tests $0 for the pattern `dev'. This yields a 0. The variable stderr, - having never been used, has a null string in it. The concatenation yields - a string value of "0" which is used as the file name. Sigh. - - I think with some more time I can come up with a decent fix, but it will - probably only print a diagnostic with -Wlint. - - Arnold - diff --git a/gnu/usr.bin/ptx/ptx.info b/gnu/usr.bin/ptx/ptx.info deleted file mode 100644 index 3bbd1bb..0000000 --- a/gnu/usr.bin/ptx/ptx.info +++ /dev/null @@ -1,496 +0,0 @@ -This is Info file ptx.info, produced by Makeinfo-1.47 from the input -file ./ptx.texinfo. - - This file documents the `ptx' command, which has the purpose of -generated permuted indices for group of files. - - Copyright (C) 1990, 1991, 1993 by the Free Software Foundation, Inc. - - Permission is granted to make and distribute verbatim copies of this -manual provided the copyright notice and this permission notice are -preserved on all copies. - - Permission is granted to copy and distribute modified versions of -this manual under the conditions for verbatim copying, provided that -the entire resulting derived work is distributed under the terms of a -permission notice identical to this one. - - Permission is granted to copy and distribute translations of this -manual into another language, under the above conditions for modified -versions, except that this permission notice may be stated in a -translation approved by the Foundation. - - -File: ptx.info, Node: Top, Next: Invoking ptx, Prev: (dir), Up: (dir) - -Introduction -************ - - This is the 0.3 beta release of `ptx', the GNU version of a permuted -index generator. This software has the main goal of providing a -replacement for the traditional `ptx' as found on System V machines, -able to handle small files quickly, while providing a platform for more -development. - - This version reimplements and extends traditional `ptx'. Among -other things, it can produce a readable "KWIC" (keywords in their -context) without the need of `nroff', there is also an option to -produce TeX compatible output. This version does not handle huge input -files, that is, those files which do not fit in memory all at once. - - *Please note* that an overall renaming of all options is -foreseeable. In fact, GNU ptx specifications are not frozen yet. - -* Menu: - -* Invoking ptx:: How to use this program -* Compatibility:: The GNU extensions to `ptx' - - -- The Detailed Node Listing -- - -How to use this program - -* General options:: Options which affect general program behaviour. -* Charset selection:: Underlying character set considerations. -* Input processing:: Input fields, contexts, and keyword selection. -* Output formatting:: Types of output format, and sizing the fields. - - -File: ptx.info, Node: Invoking ptx, Next: Compatibility, Prev: Top, Up: Top - -How to use this program -*********************** - - This tool reads a text file and essentially produces a permuted -index, with each keyword in its context. The calling sketch is one of: - - ptx [OPTION ...] [FILE ...] - - or: - - ptx -G [OPTION ...] [INPUT [OUTPUT]] - - The `-G' (or its equivalent: `--traditional') option disables all -GNU extensions and revert to traditional mode, thus introducing some -limitations, and changes several of the program's default option values. -When `-G' is not specified, GNU extensions are always enabled. GNU -extensions to `ptx' are documented wherever appropriate in this -document. See *Note Compatibility:: for an explicit list of them. - - Individual options are explained later in this document. - - When GNU extensions are enabled, there may be zero, one or several -FILE after the options. If there is no FILE, the program reads the -standard input. If there is one or several FILE, they give the name of -input files which are all read in turn, as if all the input files were -concatenated. However, there is a full contextual break between each -file and, when automatic referencing is requested, file names and line -numbers refer to individual text input files. In all cases, the -program produces the permuted index onto the standard output. - - When GNU extensions are *not* enabled, that is, when the program -operates in traditional mode, there may be zero, one or two parameters -besides the options. If there is no parameters, the program reads the -standard input and produces the permuted index onto the standard output. -If there is only one parameter, it names the text INPUT to be read -instead of the standard input. If two parameters are given, they give -respectively the name of the INPUT file to read and the name of the -OUTPUT file to produce. *Be very careful* to note that, in this case, -the contents of file given by the second parameter is destroyed. This -behaviour is dictated only by System V `ptx' compatibility, because GNU -Standards discourage output parameters not introduced by an option. - - Note that for *any* file named as the value of an option or as an -input text file, a single dash `-' may be used, in which case standard -input is assumed. However, it would not make sense to use this -convention more than once per program invocation. - -* Menu: - -* General options:: Options which affect general program behaviour. -* Charset selection:: Underlying character set considerations. -* Input processing:: Input fields, contexts, and keyword selection. -* Output formatting:: Types of output format, and sizing the fields. - - -File: ptx.info, Node: General options, Next: Charset selection, Prev: Invoking ptx, Up: Invoking ptx - -General options -=============== - -`-C' -`--copyright' - Prints a short note about the Copyright and copying conditions, - then exit without further processing. - -`-G' -`--traditional' - As already explained, this option disables all GNU extensions to - `ptx' and switch to traditional mode. - -`--help' - Prints a short help on standard output, then exit without further - processing. - -`--version' - Prints the program verison on standard output, then exit without - further processing. - - -File: ptx.info, Node: Charset selection, Next: Input processing, Prev: General options, Up: Invoking ptx - -Charset selection -================= - - As it is setup now, the program assumes that the input file is coded -using 8-bit ISO 8859-1 code, also known as Latin-1 character set, -*unless* if it is compiled for MS-DOS, in which case it uses the -character set of the IBM-PC. (GNU `ptx' is not known to work on -smaller MS-DOS machines anymore.) Compared to 7-bit ASCII, the set of -characters which are letters is then different, this fact alters the -behaviour of regular expression matching. Thus, the default regular -expression for a keyword allows foreign or diacriticized letters. -Keyword sorting, however, is still crude; it obeys the underlying -character set ordering quite blindly. - -`-f' -`--ignore-case' - Fold lower case letters to upper case for sorting. - - -File: ptx.info, Node: Input processing, Next: Output formatting, Prev: Charset selection, Up: Invoking ptx - -Word selection -============== - -`-b FILE' -`--break-file=FILE' - This option is an alternative way to option `-W' for describing - which characters make up words. This option introduces the name - of a file which contains a list of characters which can*not* be - part of one word, this file is called the "Break file". Any - character which is not part of the Break file is a word - constituent. If both options `-b' and `-W' are specified, then - `-W' has precedence and `-b' is ignored. - - When GNU extensions are enabled, the only way to avoid newline as a - break character is to write all the break characters in the file - with no newline at all, not even at the end of the file. When GNU - extensions are disabled, spaces, tabs and newlines are always - considered as break characters even if not included in the Break - file. - -`-i FILE' -`--ignore-file=FILE' - The file associated with this option contains a list of words - which will never be taken as keywords in concordance output. It - is called the "Ignore file". The file contains exactly one word - in each line; the end of line separation of words is not subject - to the value of the `-S' option. - - There is a default Ignore file used by `ptx' when this option is - not specified, usually found in `/usr/local/lib/eign' if this has - not been changed at installation time. If you want to deactivate - the default Ignore file, specify `/dev/null' instead. - -`-o FILE' -`--only-file=FILE' - The file associated with this option contains a list of words - which will be retained in concordance output, any word not - mentioned in this file is ignored. The file is called the "Only - file". The file contains exactly one word in each line; the end - of line separation of words is not subject to the value of the - `-S' option. - - There is no default for the Only file. In the case there are both - an Only file and an Ignore file, a word will be subject to be a - keyword only if it is given in the Only file and not given in the - Ignore file. - -`-r' -`--references' - On each input line, the leading sequence of non white characters - will be taken to be a reference that has the purpose of - identifying this input line on the produced permuted index. See - *Note Output formatting:: for more information about reference - production. Using this option change the default value for option - `-S'. - - Using this option, the program does not try very hard to remove - references from contexts in output, but it succeeds in doing so - *when* the context ends exactly at the newline. If option `-r' is - used with `-S' default value, or when GNU extensions are disabled, - this condition is always met and references are completely - excluded from the output contexts. - -`-S REGEXP' -`--sentence-regexp=REGEXP' - This option selects which regular expression will describe the end - of a line or the end of a sentence. In fact, there is other - distinction between end of lines or end of sentences than the - effect of this regular expression, and input line boundaries have - no special significance outside this option. By default, when GNU - extensions are enabled and if `-r' option is not used, end of - sentences are used. In this case, the precise REGEX is imported - from GNU emacs: - - [.?!][]\"')}]*\\($\\|\t\\| \\)[ \t\n]* - - Whenever GNU extensions are disabled or if `-r' option is used, end - of lines are used; in this case, the default REGEXP is just: - - \n - - Using an empty REGEXP is equivalent to completely disabling end of - line or end of sentence recognition. In this case, the whole file - is considered to be a single big line or sentence. The user might - want to disallow all truncation flag generation as well, through - option `-F ""'. *Note Syntax of Regular Expressions: - (emacs)Regexps. - - When the keywords happen to be near the beginning of the input - line or sentence, this often creates an unused area at the - beginning of the output context line; when the keywords happen to - be near the end of the input line or sentence, this often creates - an unused area at the end of the output context line. The program - tries to fill those unused areas by wrapping around context in - them; the tail of the input line or sentence is used to fill the - unused area on the left of the output line; the head of the input - line or sentence is used to fill the unused area on the right of - the output line. - - As a matter of convenience to the user, many usual backslashed - escape sequences, as found in the C language, are recognized and - converted to the corresponding characters by `ptx' itself. - -`-W REGEXP' -`--word-regexp=REGEXP' - This option selects which regular expression will describe each - keyword. By default, if GNU extensions are enabled, a word is a - sequence of letters; the REGEXP used is `\w+'. When GNU - extensions are disabled, a word is by default anything which ends - with a space, a tab or a newline; the REGEXP used is `[^ \t\n]+'. - - An empty REGEXP is equivalent to not using this option, letting the - default dive in. *Note Syntax of Regular Expressions: - (emacs)Regexps. - - As a matter of convenience to the user, many usual backslashed - escape sequences, as found in the C language, are recognized and - converted to the corresponding characters by `ptx' itself. - - -File: ptx.info, Node: Output formatting, Prev: Input processing, Up: Invoking ptx - -Output formatting -================= - - Output format is mainly controlled by `-O' and `-T' options, -described in the table below. When neither `-O' nor `-T' is selected, -and if GNU extensions are enabled, the program choose an output format -suited for a dumb terminal. Each keyword occurrence is output to the -center of one line, surrounded by its left and right contexts. Each -field is properly justified, so the concordance output could readily be -observed. As a special feature, if automatic references are selected -by option `-A' and are output before the left context, that is, if -option `-R' is *not* selected, then a colon is added after the -reference; this nicely interfaces with GNU Emacs `next-error' -processing. In this default output format, each white space character, -like newline and tab, is merely changed to exactly one space, with no -special attempt to compress consecutive spaces. This might change in -the future. Except for those white space characters, every other -character of the underlying set of 256 characters is transmitted -verbatim. - - Output format is further controlled by the following options. - -`-g NUMBER' -`--gap-size=NUMBER' - Select the size of the minimum white gap between the fields on the - output line. - -`-w NUMBER' -`--width=NUMBER' - Select the output maximum width of each final line. If references - are used, they are included or excluded from the output maximum - width depending on the value of option `-R'. If this option is not - selected, that is, when references are output before the left - context, the output maximum width takes into account the maximum - length of all references. If this options is selected, that is, - when references are output after the right context, the output - maximum width does not take into account the space taken by - references, nor the gap that precedes them. - -`-A' -`--auto-reference' - Select automatic references. Each input line will have an - automatic reference made up of the file name and the line ordinal, - with a single colon between them. However, the file name will be - empty when standard input is being read. If both `-A' and `-r' - are selected, then the input reference is still read and skipped, - but the automatic reference is used at output time, overriding the - input reference. - -`-R' -`--right-side-refs' - In default output format, when option `-R' is not used, any - reference produced by the effect of options `-r' or `-A' are given - to the far right of output lines, after the right context. In - default output format, when option `-R' is specified, references - are rather given to the beginning of each output line, before the - left context. For any other output format, option `-R' is almost - ignored, except for the fact that the width of references is *not* - taken into account in total output width given by `-w' whenever - `-R' is selected. - - This option is automatically selected whenever GNU extensions are - disabled. - -`-F STRING' -`--flac-truncation=STRING' - This option will request that any truncation in the output be - reported using the string STRING. Most output fields - theoretically extend towards the beginning or the end of the - current line, or current sentence, as selected with option `-S'. - But there is a maximum allowed output line width, changeable - through option `-w', which is further divided into space for - various output fields. When a field has to be truncated because - cannot extend until the beginning or the end of the current line - to fit in the, then a truncation occurs. By default, the string - used is a single slash, as in `-F /'. - - STRING may have more than one character, as in `-F ...'. Also, in - the particular case STRING is empty (`-F ""'), truncation flagging - is disabled, and no truncation marks are appended in this case. - - As a matter of convenience to the user, many usual backslashed - escape sequences, as found in the C language, are recognized and - converted to the corresponding characters by `ptx' itself. - -`-M STRING' -`--macro-name=STRING' - Select another STRING to be used instead of `xx', while generating - output suitable for `nroff', `troff' or TeX. - -`-O' -`--format=roff' - Choose an output format suitable for `nroff' or `troff' - processing. Each output line will look like: - - .xx "TAIL" "BEFORE" "KEYWORD_AND_AFTER" "HEAD" "REF" - - so it will be possible to write an `.xx' roff macro to take care of - the output typesetting. This is the default output format when GNU - extensions are disabled. Option `-M' might be used to change `xx' - to another macro name. - - In this output format, each non-graphical character, like newline - and tab, is merely changed to exactly one space, with no special - attempt to compress consecutive spaces. Each quote character: `"' - is doubled so it will be correctly processed by `nroff' or `troff'. - -`-T' -`--format=tex' - Choose an output format suitable for TeX processing. Each output - line will look like: - - \xx {TAIL}{BEFORE}{KEYWORD}{AFTER}{HEAD}{REF} - - so it will be possible to write write a `\xx' definition to take - care of the output typesetting. Note that when references are not - being produced, that is, neither option `-A' nor option `-r' is - selected, the last parameter of each `\xx' call is inhibited. - Option `-M' might be used to change `xx' to another macro name. - - In this output format, some special characters, like `$', `%', - `&', `#' and `_' are automatically protected with a backslash. - Curly brackets `{', `}' are also protected with a backslash, but - also enclosed in a pair of dollar signs to force mathematical - mode. The backslash itself produces the sequence `\backslash{}'. - Circumflex and tilde diacritics produce the sequence `^\{ }' and - `~\{ }' respectively. Other diacriticized characters of the - underlying character set produce an appropriate TeX sequence as - far as possible. The other non-graphical characters, like newline - and tab, and all others characters which are not part of ASCII, - are merely changed to exactly one space, with no special attempt - to compress consecutive spaces. Let me know how to improve this - special character processing for TeX. - - -File: ptx.info, Node: Compatibility, Prev: Invoking ptx, Up: Top - -The GNU extensions to `ptx' -*************************** - - This version of `ptx' contains a few features which do not exist in -System V `ptx'. These extra features are suppressed by using the `-G' -command line option, unless overridden by other command line options. -Some GNU extensions cannot be recovered by overriding, so the simple -rule is to avoid `-G' if you care about GNU extensions. Here are the -differences between this program and System V `ptx'. - - * This program can read many input files at once, it always writes - the resulting concordance on standard output. On the other end, - System V `ptx' reads only one file and produce the result on - standard output or, if a second FILE parameter is given on the - command, to that FILE. - - Having output parameters not introduced by options is a quite - dangerous practice which GNU avoids as far as possible. So, for - using `ptx' portably between GNU and System V, you should pay - attention to always use it with a single input file, and always - expect the result on standard output. You might also want to - automatically configure in a `-G' option to `ptx' calls in - products using `ptx', if the configurator finds that the installed - `ptx' accepts `-G'. - - * The only options available in System V `ptx' are options `-b', - `-f', `-g', `-i', `-o', `-r', `-t' and `-w'. All other options - are GNU extensions and are not repeated in this enumeration. - Moreover, some options have a slightly different meaning when GNU - extensions are enabled, as explained below. - - * By default, concordance output is not formatted for `troff' or - `nroff'. It is rather formatted for a dumb terminal. `troff' or - `nroff' output may still be selected through option `-O'. - - * Unless `-R' option is used, the maximum reference width is - subtracted from the total output line width. With GNU extensions - disabled, width of references is not taken into account in the - output line width computations. - - * All 256 characters, even `NUL's, are always read and processed from - input file with no adverse effect, even if GNU extensions are - disabled. However, System V `ptx' does not accept 8-bit - characters, a few control characters are rejected, and the tilda - `~' is condemned. - - * Input line length is only limited by available memory, even if GNU - extensions are disabled. However, System V `ptx' processes only - the first 200 characters in each line. - - * The break (non-word) characters default to be every character - except all letters of the underlying character set, diacriticized - or not. When GNU extensions are disabled, the break characters - default to space, tab and newline only. - - * The program makes better use of output line width. If GNU - extensions are disabled, the program rather tries to imitate - System V `ptx', but still, there are some slight disposition - glitches this program does not completely reproduce. - - * The user can specify both an Ignore file and an Only file. This - is not allowed with System V `ptx'. - - - -Tag Table: -Node: Top939 -Node: Invoking ptx2298 -Node: General options5025 -Node: Charset selection5639 -Node: Input processing6514 -Node: Output formatting12205 -Node: Compatibility18737 - -End Tag Table diff --git a/gnu/usr.bin/ptx/ptx.texinfo b/gnu/usr.bin/ptx/ptx.texinfo deleted file mode 100644 index e690c55..0000000 --- a/gnu/usr.bin/ptx/ptx.texinfo +++ /dev/null @@ -1,554 +0,0 @@ -\input texinfo @c -*-texinfo-*- -@c %**start of header -@setfilename ptx.info -@settitle GNU @code{ptx} reference manual -@finalout -@c %**end of header - -@ifinfo -This file documents the @code{ptx} command, which has the purpose of -generated permuted indices for group of files. - -Copyright (C) 1990, 1991, 1993 by the Free Software Foundation, Inc. - -Permission is granted to make and distribute verbatim copies of -this manual provided the copyright notice and this permission notice -are preserved on all copies. - -@ignore -Permission is granted to process this file through TeX and print the -results, provided the printed document carries copying permission -notice identical to this one except for the removal of this paragraph -(this paragraph not being relevant to the printed manual). - -@end ignore -Permission is granted to copy and distribute modified versions of this -manual under the conditions for verbatim copying, provided that the entire -resulting derived work is distributed under the terms of a permission -notice identical to this one. - -Permission is granted to copy and distribute translations of this manual -into another language, under the above conditions for modified versions, -except that this permission notice may be stated in a translation approved -by the Foundation. -@end ifinfo - -@titlepage -@title ptx -@subtitle The GNU permuted indexer -@subtitle Edition 0.3, for ptx version 0.3 -@subtitle November 1993 -@author by Francois Pinard - -@page -@vskip 0pt plus 1filll -Copyright @copyright{} 1990, 1991, 1993 Free Software Foundation, Inc. - -Permission is granted to make and distribute verbatim copies of -this manual provided the copyright notice and this permission notice -are preserved on all copies. - -Permission is granted to copy and distribute modified versions of this -manual under the conditions for verbatim copying, provided that the entire -resulting derived work is distributed under the terms of a permission -notice identical to this one. - -Permission is granted to copy and distribute translations of this manual -into another language, under the above conditions for modified versions, -except that this permission notice may be stated in a translation approved -by the Foundation. -@end titlepage - -@node Top, Invoking ptx, (dir), (dir) -@chapter Introduction - -This is the 0.3 beta release of @code{ptx}, the GNU version of a -permuted index generator. This software has the main goal of providing -a replacement for the traditional @code{ptx} as found on System V -machines, able to handle small files quickly, while providing a platform -for more development. - -This version reimplements and extends traditional @code{ptx}. Among -other things, it can produce a readable @dfn{KWIC} (keywords in their -context) without the need of @code{nroff}, there is also an option to -produce @TeX{} compatible output. This version does not handle huge -input files, that is, those files which do not fit in memory all at -once. - -@emph{Please note} that an overall renaming of all options is -foreseeable. In fact, GNU ptx specifications are not frozen yet. - -@menu -* Invoking ptx:: How to use this program -* Compatibility:: The GNU extensions to @code{ptx} - - --- The Detailed Node Listing --- - -How to use this program - -* General options:: Options which affect general program behaviour. -* Charset selection:: Underlying character set considerations. -* Input processing:: Input fields, contexts, and keyword selection. -* Output formatting:: Types of output format, and sizing the fields. -@end menu - -@node Invoking ptx, Compatibility, Top, Top -@chapter How to use this program - -This tool reads a text file and essentially produces a permuted index, with -each keyword in its context. The calling sketch is one of: - -@example -ptx [@var{option} @dots{}] [@var{file} @dots{}] -@end example - -or: - -@example -ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]] -@end example - -The @samp{-G} (or its equivalent: @samp{--traditional}) option disables -all GNU extensions and revert to traditional mode, thus introducing some -limitations, and changes several of the program's default option values. -When @samp{-G} is not specified, GNU extensions are always enabled. GNU -extensions to @code{ptx} are documented wherever appropriate in this -document. See @xref{Compatibility} for an explicit list of them. - -Individual options are explained later in this document. - -When GNU extensions are enabled, there may be zero, one or several -@var{file} after the options. If there is no @var{file}, the program -reads the standard input. If there is one or several @var{file}, they -give the name of input files which are all read in turn, as if all the -input files were concatenated. However, there is a full contextual -break between each file and, when automatic referencing is requested, -file names and line numbers refer to individual text input files. In -all cases, the program produces the permuted index onto the standard -output. - -When GNU extensions are @emph{not} enabled, that is, when the program -operates in traditional mode, there may be zero, one or two parameters -besides the options. If there is no parameters, the program reads the -standard input and produces the permuted index onto the standard output. -If there is only one parameter, it names the text @var{input} to be read -instead of the standard input. If two parameters are given, they give -respectively the name of the @var{input} file to read and the name of -the @var{output} file to produce. @emph{Be very careful} to note that, -in this case, the contents of file given by the second parameter is -destroyed. This behaviour is dictated only by System V @code{ptx} -compatibility, because GNU Standards discourage output parameters not -introduced by an option. - -Note that for @emph{any} file named as the value of an option or as an -input text file, a single dash @kbd{-} may be used, in which case -standard input is assumed. However, it would not make sense to use this -convention more than once per program invocation. - -@menu -* General options:: Options which affect general program behaviour. -* Charset selection:: Underlying character set considerations. -* Input processing:: Input fields, contexts, and keyword selection. -* Output formatting:: Types of output format, and sizing the fields. -@end menu - -@node General options, Charset selection, Invoking ptx, Invoking ptx -@section General options - -@table @code - -@item -C -@itemx --copyright -Prints a short note about the Copyright and copying conditions, then -exit without further processing. - -@item -G -@itemx --traditional -As already explained, this option disables all GNU extensions to -@code{ptx} and switch to traditional mode. - -@item --help -Prints a short help on standard output, then exit without further -processing. - -@item --version -Prints the program verison on standard output, then exit without further -processing. - -@end table - -@node Charset selection, Input processing, General options, Invoking ptx -@section Charset selection - -As it is setup now, the program assumes that the input file is coded -using 8-bit ISO 8859-1 code, also known as Latin-1 character set, -@emph{unless} if it is compiled for MS-DOS, in which case it uses the -character set of the IBM-PC. (GNU @code{ptx} is not known to work on -smaller MS-DOS machines anymore.) Compared to 7-bit ASCII, the set of -characters which are letters is then different, this fact alters the -behaviour of regular expression matching. Thus, the default regular -expression for a keyword allows foreign or diacriticized letters. -Keyword sorting, however, is still crude; it obeys the underlying -character set ordering quite blindly. - -@table @code - -@item -f -@itemx --ignore-case -Fold lower case letters to upper case for sorting. - -@end table - -@node Input processing, Output formatting, Charset selection, Invoking ptx -@section Word selection - -@table @code - -@item -b @var{file} -@item --break-file=@var{file} - -This option is an alternative way to option @code{-W} for describing -which characters make up words. This option introduces the name of a -file which contains a list of characters which can@emph{not} be part of -one word, this file is called the @dfn{Break file}. Any character which -is not part of the Break file is a word constituent. If both options -@code{-b} and @code{-W} are specified, then @code{-W} has precedence and -@code{-b} is ignored. - -When GNU extensions are enabled, the only way to avoid newline as a -break character is to write all the break characters in the file with no -newline at all, not even at the end of the file. When GNU extensions -are disabled, spaces, tabs and newlines are always considered as break -characters even if not included in the Break file. - -@item -i @var{file} -@itemx --ignore-file=@var{file} - -The file associated with this option contains a list of words which will -never be taken as keywords in concordance output. It is called the -@dfn{Ignore file}. The file contains exactly one word in each line; the -end of line separation of words is not subject to the value of the -@code{-S} option. - -There is a default Ignore file used by @code{ptx} when this option is -not specified, usually found in @file{/usr/local/lib/eign} if this has -not been changed at installation time. If you want to deactivate the -default Ignore file, specify @code{/dev/null} instead. - -@item -o @var{file} -@itemx --only-file=@var{file} - -The file associated with this option contains a list of words which will -be retained in concordance output, any word not mentioned in this file -is ignored. The file is called the @dfn{Only file}. The file contains -exactly one word in each line; the end of line separation of words is -not subject to the value of the @code{-S} option. - -There is no default for the Only file. In the case there are both an -Only file and an Ignore file, a word will be subject to be a keyword -only if it is given in the Only file and not given in the Ignore file. - -@item -r -@itemx --references - -On each input line, the leading sequence of non white characters will be -taken to be a reference that has the purpose of identifying this input -line on the produced permuted index. See @xref{Output formatting} for -more information about reference production. Using this option change -the default value for option @code{-S}. - -Using this option, the program does not try very hard to remove -references from contexts in output, but it succeeds in doing so -@emph{when} the context ends exactly at the newline. If option -@code{-r} is used with @code{-S} default value, or when GNU extensions -are disabled, this condition is always met and references are completely -excluded from the output contexts. - -@item -S @var{regexp} -@itemx --sentence-regexp=@var{regexp} - -This option selects which regular expression will describe the end of a -line or the end of a sentence. In fact, there is other distinction -between end of lines or end of sentences than the effect of this regular -expression, and input line boundaries have no special significance -outside this option. By default, when GNU extensions are enabled and if -@code{-r} option is not used, end of sentences are used. In this -case, the precise @var{regex} is imported from GNU emacs: - -@example -[.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]* -@end example - -Whenever GNU extensions are disabled or if @code{-r} option is used, end -of lines are used; in this case, the default @var{regexp} is just: - -@example -\n -@end example - -Using an empty REGEXP is equivalent to completely disabling end of line or end -of sentence recognition. In this case, the whole file is considered to -be a single big line or sentence. The user might want to disallow all -truncation flag generation as well, through option @code{-F ""}. -@xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs -Manual}. - -When the keywords happen to be near the beginning of the input line or -sentence, this often creates an unused area at the beginning of the -output context line; when the keywords happen to be near the end of the -input line or sentence, this often creates an unused area at the end of -the output context line. The program tries to fill those unused areas -by wrapping around context in them; the tail of the input line or -sentence is used to fill the unused area on the left of the output line; -the head of the input line or sentence is used to fill the unused area -on the right of the output line. - -As a matter of convenience to the user, many usual backslashed escape -sequences, as found in the C language, are recognized and converted to -the corresponding characters by @code{ptx} itself. - -@item -W @var{regexp} -@itemx --word-regexp=@var{regexp} - -This option selects which regular expression will describe each keyword. -By default, if GNU extensions are enabled, a word is a sequence of -letters; the @var{regexp} used is @code{\w+}. When GNU extensions are -disabled, a word is by default anything which ends with a space, a tab -or a newline; the @var{regexp} used is @code{[^ \t\n]+}. - -An empty REGEXP is equivalent to not using this option, letting the -default dive in. @xref{Regexps, , Syntax of Regular Expressions, emacs, -The GNU Emacs Manual}. - -As a matter of convenience to the user, many usual backslashed escape -sequences, as found in the C language, are recognized and converted to -the corresponding characters by @code{ptx} itself. - -@end table - -@node Output formatting, , Input processing, Invoking ptx -@section Output formatting - -Output format is mainly controlled by @code{-O} and @code{-T} options, -described in the table below. When neither @code{-O} nor @code{-T} is -selected, and if GNU extensions are enabled, the program choose an -output format suited for a dumb terminal. Each keyword occurrence is -output to the center of one line, surrounded by its left and right -contexts. Each field is properly justified, so the concordance output -could readily be observed. As a special feature, if automatic -references are selected by option @code{-A} and are output before the -left context, that is, if option @code{-R} is @emph{not} selected, then -a colon is added after the reference; this nicely interfaces with GNU -Emacs @code{next-error} processing. In this default output format, each -white space character, like newline and tab, is merely changed to -exactly one space, with no special attempt to compress consecutive -spaces. This might change in the future. Except for those white space -characters, every other character of the underlying set of 256 -characters is transmitted verbatim. - -Output format is further controlled by the following options. - -@table @code - -@item -g @var{number} -@itemx --gap-size=@var{number} - -Select the size of the minimum white gap between the fields on the output -line. - -@item -w @var{number} -@itemx --width=@var{number} - -Select the output maximum width of each final line. If references are -used, they are included or excluded from the output maximum width -depending on the value of option @code{-R}. If this option is not -selected, that is, when references are output before the left context, -the output maximum width takes into account the maximum length of all -references. If this options is selected, that is, when references are -output after the right context, the output maximum width does not take -into account the space taken by references, nor the gap that precedes -them. - -@item -A -@itemx --auto-reference - -Select automatic references. Each input line will have an automatic -reference made up of the file name and the line ordinal, with a single -colon between them. However, the file name will be empty when standard -input is being read. If both @code{-A} and @code{-r} are selected, then -the input reference is still read and skipped, but the automatic -reference is used at output time, overriding the input reference. - -@item -R -@itemx --right-side-refs - -In default output format, when option @code{-R} is not used, any -reference produced by the effect of options @code{-r} or @code{-A} are -given to the far right of output lines, after the right context. In -default output format, when option @code{-R} is specified, references -are rather given to the beginning of each output line, before the left -context. For any other output format, option @code{-R} is almost -ignored, except for the fact that the width of references is @emph{not} -taken into account in total output width given by @code{-w} whenever -@code{-R} is selected. - -This option is automatically selected whenever GNU extensions are -disabled. - -@item -F @var{string} -@itemx --flac-truncation=@var{string} - -This option will request that any truncation in the output be reported -using the string @var{string}. Most output fields theoretically extend -towards the beginning or the end of the current line, or current -sentence, as selected with option @code{-S}. But there is a maximum -allowed output line width, changeable through option @code{-w}, which is -further divided into space for various output fields. When a field has -to be truncated because cannot extend until the beginning or the end of -the current line to fit in the, then a truncation occurs. By default, -the string used is a single slash, as in @code{-F /}. - -@var{string} may have more than one character, as in @code{-F ...}. -Also, in the particular case @var{string} is empty (@code{-F ""}), -truncation flagging is disabled, and no truncation marks are appended in -this case. - -As a matter of convenience to the user, many usual backslashed escape -sequences, as found in the C language, are recognized and converted to -the corresponding characters by @code{ptx} itself. - -@item -M @var{string} -@itemx --macro-name=@var{string} - -Select another @var{string} to be used instead of @samp{xx}, while -generating output suitable for @code{nroff}, @code{troff} or @TeX{}. - -@item -O -@itemx --format=roff - -Choose an output format suitable for @code{nroff} or @code{troff} -processing. Each output line will look like: - -@example -.xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}" -@end example - -so it will be possible to write an @samp{.xx} roff macro to take care of -the output typesetting. This is the default output format when GNU -extensions are disabled. Option @samp{-M} might be used to change -@samp{xx} to another macro name. - -In this output format, each non-graphical character, like newline and -tab, is merely changed to exactly one space, with no special attempt to -compress consecutive spaces. Each quote character: @kbd{"} is doubled -so it will be correctly processed by @code{nroff} or @code{troff}. - -@item -T -@itemx --format=tex - -Choose an output format suitable for @TeX{} processing. Each output -line will look like: - -@example -\xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@} -@end example - -@noindent -so it will be possible to write write a @code{\xx} definition to take -care of the output typesetting. Note that when references are not being -produced, that is, neither option @code{-A} nor option @code{-r} is -selected, the last parameter of each @code{\xx} call is inhibited. -Option @samp{-M} might be used to change @samp{xx} to another macro -name. - -In this output format, some special characters, like @kbd{$}, @kbd{%}, -@kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a -backslash. Curly brackets @kbd{@{}, @kbd{@}} are also protected with a -backslash, but also enclosed in a pair of dollar signs to force -mathematical mode. The backslash itself produces the sequence -@code{\backslash@{@}}. Circumflex and tilde diacritics produce the -sequence @code{^\@{ @}} and @code{~\@{ @}} respectively. Other -diacriticized characters of the underlying character set produce an -appropriate @TeX{} sequence as far as possible. The other non-graphical -characters, like newline and tab, and all others characters which are -not part of ASCII, are merely changed to exactly one space, with no -special attempt to compress consecutive spaces. Let me know how to -improve this special character processing for @TeX{}. - -@end table - -@node Compatibility, , Invoking ptx, Top -@chapter The GNU extensions to @code{ptx} - -This version of @code{ptx} contains a few features which do not exist in -System V @code{ptx}. These extra features are suppressed by using the -@samp{-G} command line option, unless overridden by other command line -options. Some GNU extensions cannot be recovered by overriding, so the -simple rule is to avoid @samp{-G} if you care about GNU extensions. -Here are the differences between this program and System V @code{ptx}. - -@itemize @bullet - -@item -This program can read many input files at once, it always writes the -resulting concordance on standard output. On the other end, System V -@code{ptx} reads only one file and produce the result on standard output -or, if a second @var{file} parameter is given on the command, to that -@var{file}. - -Having output parameters not introduced by options is a quite dangerous -practice which GNU avoids as far as possible. So, for using @code{ptx} -portably between GNU and System V, you should pay attention to always -use it with a single input file, and always expect the result on -standard output. You might also want to automatically configure in a -@samp{-G} option to @code{ptx} calls in products using @code{ptx}, if -the configurator finds that the installed @code{ptx} accepts @samp{-G}. - -@item -The only options available in System V @code{ptx} are options @samp{-b}, -@samp{-f}, @samp{-g}, @samp{-i}, @samp{-o}, @samp{-r}, @samp{-t} and -@samp{-w}. All other options are GNU extensions and are not repeated in -this enumeration. Moreover, some options have a slightly different -meaning when GNU extensions are enabled, as explained below. - -@item -By default, concordance output is not formatted for @code{troff} or -@code{nroff}. It is rather formatted for a dumb terminal. @code{troff} -or @code{nroff} output may still be selected through option @code{-O}. - -@item -Unless @code{-R} option is used, the maximum reference width is -subtracted from the total output line width. With GNU extensions -disabled, width of references is not taken into account in the output -line width computations. - -@item -All 256 characters, even @kbd{NUL}s, are always read and processed from -input file with no adverse effect, even if GNU extensions are disabled. -However, System V @code{ptx} does not accept 8-bit characters, a few -control characters are rejected, and the tilda @kbd{~} is condemned. - -@item -Input line length is only limited by available memory, even if GNU -extensions are disabled. However, System V @code{ptx} processes only -the first 200 characters in each line. - -@item -The break (non-word) characters default to be every character except all -letters of the underlying character set, diacriticized or not. When GNU -extensions are disabled, the break characters default to space, tab and -newline only. - -@item -The program makes better use of output line width. If GNU extensions -are disabled, the program rather tries to imitate System V @code{ptx}, -but still, there are some slight disposition glitches this program does -not completely reproduce. - -@item -The user can specify both an Ignore file and an Only file. This is not -allowed with System V @code{ptx}. - -@end itemize - -@bye diff --git a/gnu/usr.bin/tar/regex.h b/gnu/usr.bin/tar/regex.h deleted file mode 100644 index 0840861..0000000 --- a/gnu/usr.bin/tar/regex.h +++ /dev/null @@ -1,490 +0,0 @@ -/* Definitions for data structures and routines for the regular - expression library, version 0.11. - - Copyright (C) 1985, 89, 90, 91, 92 Free Software Foundation, Inc. - - This program is free software; you can redistribute it and/or modify - it under the terms of the GNU General Public License as published by - the Free Software Foundation; either version 2, or (at your option) - any later version. - - This program is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - GNU General Public License for more details. - - You should have received a copy of the GNU General Public License - along with this program; if not, write to the Free Software - Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ - -#ifndef __REGEXP_LIBRARY_H__ -#define __REGEXP_LIBRARY_H__ - -/* POSIX says that <sys/types.h> must be included (by the caller) before - <regex.h>. */ - -#ifdef VMS -/* VMS doesn't have `size_t' in <sys/types.h>, even though POSIX says it - should be there. */ -#include <stddef.h> -#endif - - -/* The following bits are used to determine the regexp syntax we - recognize. The set/not-set meanings are chosen so that Emacs syntax - remains the value 0. The bits are given in alphabetical order, and - the definitions shifted by one from the previous bit; thus, when we - add or remove a bit, only one other definition need change. */ -typedef unsigned reg_syntax_t; - -/* If this bit is not set, then \ inside a bracket expression is literal. - If set, then such a \ quotes the following character. */ -#define RE_BACKSLASH_ESCAPE_IN_LISTS (1) - -/* If this bit is not set, then + and ? are operators, and \+ and \? are - literals. - If set, then \+ and \? are operators and + and ? are literals. */ -#define RE_BK_PLUS_QM (RE_BACKSLASH_ESCAPE_IN_LISTS << 1) - -/* If this bit is set, then character classes are supported. They are: - [:alpha:], [:upper:], [:lower:], [:digit:], [:alnum:], [:xdigit:], - [:space:], [:print:], [:punct:], [:graph:], and [:cntrl:]. - If not set, then character classes are not supported. */ -#define RE_CHAR_CLASSES (RE_BK_PLUS_QM << 1) - -/* If this bit is set, then ^ and $ are always anchors (outside bracket - expressions, of course). - If this bit is not set, then it depends: - ^ is an anchor if it is at the beginning of a regular - expression or after an open-group or an alternation operator; - $ is an anchor if it is at the end of a regular expression, or - before a close-group or an alternation operator. - - This bit could be (re)combined with RE_CONTEXT_INDEP_OPS, because - POSIX draft 11.2 says that * etc. in leading positions is undefined. - We already implemented a previous draft which made those constructs - invalid, though, so we haven't changed the code back. */ -#define RE_CONTEXT_INDEP_ANCHORS (RE_CHAR_CLASSES << 1) - -/* If this bit is set, then special characters are always special - regardless of where they are in the pattern. - If this bit is not set, then special characters are special only in - some contexts; otherwise they are ordinary. Specifically, - * + ? and intervals are only special when not after the beginning, - open-group, or alternation operator. */ -#define RE_CONTEXT_INDEP_OPS (RE_CONTEXT_INDEP_ANCHORS << 1) - -/* If this bit is set, then *, +, ?, and { cannot be first in an re or - immediately after an alternation or begin-group operator. */ -#define RE_CONTEXT_INVALID_OPS (RE_CONTEXT_INDEP_OPS << 1) - -/* If this bit is set, then . matches newline. - If not set, then it doesn't. */ -#define RE_DOT_NEWLINE (RE_CONTEXT_INVALID_OPS << 1) - -/* If this bit is set, then . doesn't match NUL. - If not set, then it does. */ -#define RE_DOT_NOT_NULL (RE_DOT_NEWLINE << 1) - -/* If this bit is set, nonmatching lists [^...] do not match newline. - If not set, they do. */ -#define RE_HAT_LISTS_NOT_NEWLINE (RE_DOT_NOT_NULL << 1) - -/* If this bit is set, either \{...\} or {...} defines an - interval, depending on RE_NO_BK_BRACES. - If not set, \{, \}, {, and } are literals. */ -#define RE_INTERVALS (RE_HAT_LISTS_NOT_NEWLINE << 1) - -/* If this bit is set, +, ? and | aren't recognized as operators. - If not set, they are. */ -#define RE_LIMITED_OPS (RE_INTERVALS << 1) - -/* If this bit is set, newline is an alternation operator. - If not set, newline is literal. */ -#define RE_NEWLINE_ALT (RE_LIMITED_OPS << 1) - -/* If this bit is set, then `{...}' defines an interval, and \{ and \} - are literals. - If not set, then `\{...\}' defines an interval. */ -#define RE_NO_BK_BRACES (RE_NEWLINE_ALT << 1) - -/* If this bit is set, (...) defines a group, and \( and \) are literals. - If not set, \(...\) defines a group, and ( and ) are literals. */ -#define RE_NO_BK_PARENS (RE_NO_BK_BRACES << 1) - -/* If this bit is set, then \<digit> matches <digit>. - If not set, then \<digit> is a back-reference. */ -#define RE_NO_BK_REFS (RE_NO_BK_PARENS << 1) - -/* If this bit is set, then | is an alternation operator, and \| is literal. - If not set, then \| is an alternation operator, and | is literal. */ -#define RE_NO_BK_VBAR (RE_NO_BK_REFS << 1) - -/* If this bit is set, then an ending range point collating higher - than the starting range point, as in [z-a], is invalid. - If not set, then when ending range point collates higher than the - starting range point, the range is ignored. */ -#define RE_NO_EMPTY_RANGES (RE_NO_BK_VBAR << 1) - -/* If this bit is set, then an unmatched ) is ordinary. - If not set, then an unmatched ) is invalid. */ -#define RE_UNMATCHED_RIGHT_PAREN_ORD (RE_NO_EMPTY_RANGES << 1) - -/* This global variable defines the particular regexp syntax to use (for - some interfaces). When a regexp is compiled, the syntax used is - stored in the pattern buffer, so changing this does not affect - already-compiled regexps. */ -extern reg_syntax_t re_syntax_options; - -/* Define combinations of the above bits for the standard possibilities. - (The [[[ comments delimit what gets put into the Texinfo file, so - don't delete them!) */ -/* [[[begin syntaxes]]] */ -#define RE_SYNTAX_EMACS 0 - -#define RE_SYNTAX_AWK \ - (RE_BACKSLASH_ESCAPE_IN_LISTS | RE_DOT_NOT_NULL \ - | RE_NO_BK_PARENS | RE_NO_BK_REFS \ - | RE_NO_BK_VBAR | RE_NO_EMPTY_RANGES \ - | RE_UNMATCHED_RIGHT_PAREN_ORD) - -#define RE_SYNTAX_POSIX_AWK \ - (RE_SYNTAX_POSIX_EXTENDED | RE_BACKSLASH_ESCAPE_IN_LISTS) - -#define RE_SYNTAX_GREP \ - (RE_BK_PLUS_QM | RE_CHAR_CLASSES \ - | RE_HAT_LISTS_NOT_NEWLINE | RE_INTERVALS \ - | RE_NEWLINE_ALT) - -#define RE_SYNTAX_EGREP \ - (RE_CHAR_CLASSES | RE_CONTEXT_INDEP_ANCHORS \ - | RE_CONTEXT_INDEP_OPS | RE_HAT_LISTS_NOT_NEWLINE \ - | RE_NEWLINE_ALT | RE_NO_BK_PARENS \ - | RE_NO_BK_VBAR) - -#define RE_SYNTAX_POSIX_EGREP \ - (RE_SYNTAX_EGREP | RE_INTERVALS | RE_NO_BK_BRACES) - -/* P1003.2/D11.2, section 4.20.7.1, lines 5078ff. */ -#define RE_SYNTAX_ED RE_SYNTAX_POSIX_BASIC - -#define RE_SYNTAX_SED RE_SYNTAX_POSIX_BASIC - -/* Syntax bits common to both basic and extended POSIX regex syntax. */ -#define _RE_SYNTAX_POSIX_COMMON \ - (RE_CHAR_CLASSES | RE_DOT_NEWLINE | RE_DOT_NOT_NULL \ - | RE_INTERVALS | RE_NO_EMPTY_RANGES) - -#define RE_SYNTAX_POSIX_BASIC \ - (_RE_SYNTAX_POSIX_COMMON | RE_BK_PLUS_QM) - -/* Differs from ..._POSIX_BASIC only in that RE_BK_PLUS_QM becomes - RE_LIMITED_OPS, i.e., \? \+ \| are not recognized. Actually, this - isn't minimal, since other operators, such as \`, aren't disabled. */ -#define RE_SYNTAX_POSIX_MINIMAL_BASIC \ - (_RE_SYNTAX_POSIX_COMMON | RE_LIMITED_OPS) - -#define RE_SYNTAX_POSIX_EXTENDED \ - (_RE_SYNTAX_POSIX_COMMON | RE_CONTEXT_INDEP_ANCHORS \ - | RE_CONTEXT_INDEP_OPS | RE_NO_BK_BRACES \ - | RE_NO_BK_PARENS | RE_NO_BK_VBAR \ - | RE_UNMATCHED_RIGHT_PAREN_ORD) - -/* Differs from ..._POSIX_EXTENDED in that RE_CONTEXT_INVALID_OPS - replaces RE_CONTEXT_INDEP_OPS and RE_NO_BK_REFS is added. */ -#define RE_SYNTAX_POSIX_MINIMAL_EXTENDED \ - (_RE_SYNTAX_POSIX_COMMON | RE_CONTEXT_INDEP_ANCHORS \ - | RE_CONTEXT_INVALID_OPS | RE_NO_BK_BRACES \ - | RE_NO_BK_PARENS | RE_NO_BK_REFS \ - | RE_NO_BK_VBAR | RE_UNMATCHED_RIGHT_PAREN_ORD) -/* [[[end syntaxes]]] */ - -/* Maximum number of duplicates an interval can allow. Some systems - (erroneously) define this in other header files, but we want our - value, so remove any previous define. */ -#ifdef RE_DUP_MAX -#undef RE_DUP_MAX -#endif -#define RE_DUP_MAX ((1 << 15) - 1) - - -/* POSIX `cflags' bits (i.e., information for `regcomp'). */ - -/* If this bit is set, then use extended regular expression syntax. - If not set, then use basic regular expression syntax. */ -#define REG_EXTENDED 1 - -/* If this bit is set, then ignore case when matching. - If not set, then case is significant. */ -#define REG_ICASE (REG_EXTENDED << 1) - -/* If this bit is set, then anchors do not match at newline - characters in the string. - If not set, then anchors do match at newlines. */ -#define REG_NEWLINE (REG_ICASE << 1) - -/* If this bit is set, then report only success or fail in regexec. - If not set, then returns differ between not matching and errors. */ -#define REG_NOSUB (REG_NEWLINE << 1) - - -/* POSIX `eflags' bits (i.e., information for regexec). */ - -/* If this bit is set, then the beginning-of-line operator doesn't match - the beginning of the string (presumably because it's not the - beginning of a line). - If not set, then the beginning-of-line operator does match the - beginning of the string. */ -#define REG_NOTBOL 1 - -/* Like REG_NOTBOL, except for the end-of-line. */ -#define REG_NOTEOL (1 << 1) - - -/* If any error codes are removed, changed, or added, update the - `re_error_msg' table in regex.c. */ -typedef enum -{ - REG_NOERROR = 0, /* Success. */ - REG_NOMATCH, /* Didn't find a match (for regexec). */ - - /* POSIX regcomp return error codes. (In the order listed in the - standard.) */ - REG_BADPAT, /* Invalid pattern. */ - REG_ECOLLATE, /* Not implemented. */ - REG_ECTYPE, /* Invalid character class name. */ - REG_EESCAPE, /* Trailing backslash. */ - REG_ESUBREG, /* Invalid back reference. */ - REG_EBRACK, /* Unmatched left bracket. */ - REG_EPAREN, /* Parenthesis imbalance. */ - REG_EBRACE, /* Unmatched \{. */ - REG_BADBR, /* Invalid contents of \{\}. */ - REG_ERANGE, /* Invalid range end. */ - REG_ESPACE, /* Ran out of memory. */ - REG_BADRPT, /* No preceding re for repetition op. */ - - /* Error codes we've added. */ - REG_EEND, /* Premature end. */ - REG_ESIZE, /* Compiled pattern bigger than 2^16 bytes. */ - REG_ERPAREN /* Unmatched ) or \); not returned from regcomp. */ -} reg_errcode_t; - -/* This data structure represents a compiled pattern. Before calling - the pattern compiler, the fields `buffer', `allocated', `fastmap', - `translate', and `no_sub' can be set. After the pattern has been - compiled, the `re_nsub' field is available. All other fields are - private to the regex routines. */ - -struct re_pattern_buffer -{ -/* [[[begin pattern_buffer]]] */ - /* Space that holds the compiled pattern. It is declared as - `unsigned char *' because its elements are - sometimes used as array indexes. */ - unsigned char *buffer; - - /* Number of bytes to which `buffer' points. */ - unsigned long allocated; - - /* Number of bytes actually used in `buffer'. */ - unsigned long used; - - /* Syntax setting with which the pattern was compiled. */ - reg_syntax_t syntax; - - /* Pointer to a fastmap, if any, otherwise zero. re_search uses - the fastmap, if there is one, to skip over impossible - starting points for matches. */ - char *fastmap; - - /* Either a translate table to apply to all characters before - comparing them, or zero for no translation. The translation - is applied to a pattern when it is compiled and to a string - when it is matched. */ - char *translate; - - /* Number of subexpressions found by the compiler. */ - size_t re_nsub; - - /* Zero if this pattern cannot match the empty string, one else. - Well, in truth it's used only in `re_search_2', to see - whether or not we should use the fastmap, so we don't set - this absolutely perfectly; see `re_compile_fastmap' (the - `duplicate' case). */ - unsigned can_be_null : 1; - - /* If REGS_UNALLOCATED, allocate space in the `regs' structure - for `max (RE_NREGS, re_nsub + 1)' groups. - If REGS_REALLOCATE, reallocate space if necessary. - If REGS_FIXED, use what's there. */ -#define REGS_UNALLOCATED 0 -#define REGS_REALLOCATE 1 -#define REGS_FIXED 2 - unsigned regs_allocated : 2; - - /* Set to zero when `regex_compile' compiles a pattern; set to one - by `re_compile_fastmap' if it updates the fastmap. */ - unsigned fastmap_accurate : 1; - - /* If set, `re_match_2' does not return information about - subexpressions. */ - unsigned no_sub : 1; - - /* If set, a beginning-of-line anchor doesn't match at the - beginning of the string. */ - unsigned not_bol : 1; - - /* Similarly for an end-of-line anchor. */ - unsigned not_eol : 1; - - /* If true, an anchor at a newline matches. */ - unsigned newline_anchor : 1; - -/* [[[end pattern_buffer]]] */ -}; - -typedef struct re_pattern_buffer regex_t; - - -/* search.c (search_buffer) in Emacs needs this one opcode value. It is - defined both in `regex.c' and here. */ -#define RE_EXACTN_VALUE 1 - -/* Type for byte offsets within the string. POSIX mandates this. */ -typedef int regoff_t; - - -/* This is the structure we store register match data in. See - regex.texinfo for a full description of what registers match. */ -struct re_registers -{ - unsigned num_regs; - regoff_t *start; - regoff_t *end; -}; - - -/* If `regs_allocated' is REGS_UNALLOCATED in the pattern buffer, - `re_match_2' returns information about at least this many registers - the first time a `regs' structure is passed. */ -#ifndef RE_NREGS -#define RE_NREGS 30 -#endif - - -/* POSIX specification for registers. Aside from the different names than - `re_registers', POSIX uses an array of structures, instead of a - structure of arrays. */ -typedef struct -{ - regoff_t rm_so; /* Byte offset from string's start to substring's start. */ - regoff_t rm_eo; /* Byte offset from string's start to substring's end. */ -} regmatch_t; - -/* Declarations for routines. */ - -/* To avoid duplicating every routine declaration -- once with a - prototype (if we are ANSI), and once without (if we aren't) -- we - use the following macro to declare argument types. This - unfortunately clutters up the declarations a bit, but I think it's - worth it. */ - -#if __STDC__ - -#define _RE_ARGS(args) args - -#else /* not __STDC__ */ - -#define _RE_ARGS(args) () - -#endif /* not __STDC__ */ - -/* Sets the current default syntax to SYNTAX, and return the old syntax. - You can also simply assign to the `re_syntax_options' variable. */ -extern reg_syntax_t re_set_syntax _RE_ARGS ((reg_syntax_t syntax)); - -/* Compile the regular expression PATTERN, with length LENGTH - and syntax given by the global `re_syntax_options', into the buffer - BUFFER. Return NULL if successful, and an error string if not. */ -extern const char *re_compile_pattern - _RE_ARGS ((const char *pattern, int length, - struct re_pattern_buffer *buffer)); - - -/* Compile a fastmap for the compiled pattern in BUFFER; used to - accelerate searches. Return 0 if successful and -2 if was an - internal error. */ -extern int re_compile_fastmap _RE_ARGS ((struct re_pattern_buffer *buffer)); - - -/* Search in the string STRING (with length LENGTH) for the pattern - compiled into BUFFER. Start searching at position START, for RANGE - characters. Return the starting position of the match, -1 for no - match, or -2 for an internal error. Also return register - information in REGS (if REGS and BUFFER->no_sub are nonzero). */ -extern int re_search - _RE_ARGS ((struct re_pattern_buffer *buffer, const char *string, - int length, int start, int range, struct re_registers *regs)); - - -/* Like `re_search', but search in the concatenation of STRING1 and - STRING2. Also, stop searching at index START + STOP. */ -extern int re_search_2 - _RE_ARGS ((struct re_pattern_buffer *buffer, const char *string1, - int length1, const char *string2, int length2, - int start, int range, struct re_registers *regs, int stop)); - - -/* Like `re_search', but return how many characters in STRING the regexp - in BUFFER matched, starting at position START. */ -extern int re_match - _RE_ARGS ((struct re_pattern_buffer *buffer, const char *string, - int length, int start, struct re_registers *regs)); - - -/* Relates to `re_match' as `re_search_2' relates to `re_search'. */ -extern int re_match_2 - _RE_ARGS ((struct re_pattern_buffer *buffer, const char *string1, - int length1, const char *string2, int length2, - int start, struct re_registers *regs, int stop)); - - -/* Set REGS to hold NUM_REGS registers, storing them in STARTS and - ENDS. Subsequent matches using BUFFER and REGS will use this memory - for recording register information. STARTS and ENDS must be - allocated with malloc, and must each be at least `NUM_REGS * sizeof - (regoff_t)' bytes long. - - If NUM_REGS == 0, then subsequent matches should allocate their own - register data. - - Unless this function is called, the first search or match using - PATTERN_BUFFER will allocate its own register data, without - freeing the old data. */ -extern void re_set_registers - _RE_ARGS ((struct re_pattern_buffer *buffer, struct re_registers *regs, - unsigned num_regs, regoff_t *starts, regoff_t *ends)); - -/* 4.2 bsd compatibility. */ -extern char *re_comp _RE_ARGS ((const char *)); -extern int re_exec _RE_ARGS ((const char *)); - -/* POSIX compatibility. */ -extern int regcomp _RE_ARGS ((regex_t *preg, const char *pattern, int cflags)); -extern int regexec - _RE_ARGS ((const regex_t *preg, const char *string, size_t nmatch, - regmatch_t pmatch[], int eflags)); -extern size_t regerror - _RE_ARGS ((int errcode, const regex_t *preg, char *errbuf, - size_t errbuf_size)); -extern void regfree _RE_ARGS ((regex_t *preg)); - -#endif /* not __REGEXP_LIBRARY_H__ */ - -/* -Local variables: -make-backup-files: t -version-control: t -trim-versions-without-asking: nil -End: -*/ diff --git a/gnu/usr.bin/tar/y.tab.h b/gnu/usr.bin/tar/y.tab.h deleted file mode 100644 index 4a541d2..0000000 --- a/gnu/usr.bin/tar/y.tab.h +++ /dev/null @@ -1,18 +0,0 @@ -#define tAGO 257 -#define tDAY 258 -#define tDAYZONE 259 -#define tID 260 -#define tMERIDIAN 261 -#define tMINUTE_UNIT 262 -#define tMONTH 263 -#define tMONTH_UNIT 264 -#define tSEC_UNIT 265 -#define tSNUMBER 266 -#define tUNUMBER 267 -#define tZONE 268 -#define tDST 269 -typedef union { - time_t Number; - enum _MERIDIAN Meridian; -} YYSTYPE; -extern YYSTYPE yylval; |