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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Klaus Klein.
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.Dd January 26, 2005
.Dt NL 1
.Os
.Sh NAME
.Nm nl
.Nd line numbering filter
.Sh SYNOPSIS
.Nm
.Op Fl p
.Bk -words
.Op Fl b Ar type
.Ek
.Bk -words
.Op Fl d Ar delim
.Ek
.Bk -words
.Op Fl f Ar type
.Ek
.Bk -words
.Op Fl h Ar type
.Ek
.Bk -words
.Op Fl i Ar incr
.Ek
.Bk -words
.Op Fl l Ar num
.Ek
.Bk -words
.Op Fl n Ar format
.Ek
.Bk -words
.Op Fl s Ar sep
.Ek
.Bk -words
.Op Fl v Ar startnum
.Ek
.Bk -words
.Op Fl w Ar width
.Ek
.Op Ar file
.Sh DESCRIPTION
The
.Nm
utility reads lines from the named
.Ar file
or the standard input if the
.Ar file
argument is omitted,
applies a configurable line numbering filter operation and writes the result
to the standard output.
.Pp
The
.Nm
utility treats the text it reads in terms of logical pages.
Unless specified otherwise, line numbering is reset at the start of each
logical page.
A logical page consists of a header, a body and a footer
section; empty sections are valid.
Different line numbering options are
independently available for header, body and footer sections.
.Pp
The starts of logical page sections are signalled by input lines containing
nothing but one of the following sequences of delimiter characters:
.Bl -column "\e:\e:\e:" "Start of" -offset indent
.Em "Line	Start of"
.It "\e:\e:\e:	header"
.It "\e:\e:	body"
.It "\e:	footer"
.El
.Pp
If the input does not contain any logical page section signalling directives,
the text being read is assumed to consist of a single logical page body.
.Pp
The following options are available:
.Bl -tag -width ".Fl v Ar startnum"
.It Fl b Ar type
Specify the logical page body lines to be numbered.
Recognized
.Ar type
arguments are:
.Bl -tag -width indent
.It Cm a
Number all lines.
.It Cm t
Number only non-empty lines.
.It Cm n
No line numbering.
.It Cm p Ns Ar expr
Number only those lines that contain the basic regular expression specified
by
.Ar expr .
.El
.Pp
The default
.Ar type
for logical page body lines is
.Cm t .
.It Fl d Ar delim
Specify the delimiter characters used to indicate the start of a logical
page section in the input file.
At most two characters may be specified;
if only one character is specified, the first character is replaced and the
second character remains unchanged.
The default
.Ar delim
characters are
.Dq Li \e: .
.It Fl f Ar type
Specify the same as
.Fl b Ar type
except for logical page footer lines.
The default
.Ar type
for logical page footer lines is
.Cm n .
.It Fl h Ar type
Specify the same as
.Fl b Ar type
except for logical page header lines.
The default
.Ar type
for logical page header lines is
.Cm n .
.It Fl i Ar incr
Specify the increment value used to number logical page lines.
The default
.Ar incr
value is 1.
.It Fl l Ar num
If numbering of all lines is specified for the current logical section
using the corresponding
.Fl b Cm a ,
.Fl f Cm a
or
.Fl h Cm a
option,
specify the number of adjacent blank lines to be considered as one.
For example,
.Fl l
2 results in only the second adjacent blank line being numbered.
The default
.Ar num
value is 1.
.It Fl n Ar format
Specify the line numbering output format.
Recognized
.Ar format
arguments are:
.Bl -tag -width indent -compact
.It Cm ln
Left justified.
.It Cm rn
Right justified, leading zeros suppressed.
.It Cm rz
Right justified, leading zeros kept.
.El
.Pp
The default
.Ar format
is
.Cm rn .
.It Fl p
Specify that line numbering should not be restarted at logical page delimiters.
.It Fl s Ar sep
Specify the characters used in separating the line number and the corresponding
text line.
The default
.Ar sep
setting is a single tab character.
.It Fl v Ar startnum
Specify the initial value used to number logical page lines; see also the
description of the
.Fl p
option.
The default
.Ar startnum
value is 1.
.It Fl w Ar width
Specify the number of characters to be occupied by the line number;
in case the
.Ar width
is insufficient to hold the line number, it will be truncated to its
.Ar width
least significant digits.
The default
.Ar width
is 6.
.El
.Sh ENVIRONMENT
The
.Ev LANG , LC_ALL , LC_CTYPE
and
.Ev LC_COLLATE
environment variables affect the execution of
.Nm
as described in
.Xr environ 7 .
.Sh EXIT STATUS
.Ex -std
.Sh SEE ALSO
.Xr jot 1 ,
.Xr pr 1
.Sh STANDARDS
The
.Nm
utility conforms to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Nm
utility first appeared in
.At V.2 .
.Sh BUGS
Input lines are limited to
.Dv LINE_MAX
(2048) bytes in length.