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author | jilles <jilles@FreeBSD.org> | 2011-05-05 20:55:55 +0000 |
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committer | jilles <jilles@FreeBSD.org> | 2011-05-05 20:55:55 +0000 |
commit | 5a49f52603051288db09536911ad4c73579aeb99 (patch) | |
tree | f65bdb50369c1f6631b70c1264abbc69f9ce4513 /bin/sh/sh.1 | |
parent | 7ec44d66a6202d6f9bf5a7ef04ba108896f96bea (diff) | |
download | FreeBSD-src-5a49f52603051288db09536911ad4c73579aeb99.zip FreeBSD-src-5a49f52603051288db09536911ad4c73579aeb99.tar.gz |
sh: Add $'quoting' (C-style escape sequences).
A string between $' and ' may contain backslash escape sequences similar to
the ones in a C string constant (except that a single-quote must be escaped
and a double-quote need not be). Details are in the sh(1) man page.
This construct is useful to include unprintable characters, tabs and
newlines in strings; while this can be done with a command substitution
containing a printf command, that needs ugly workarounds if the result is to
end with a newline as command substitution removes all trailing newlines.
The construct may also be useful in future to describe unprintable
characters without needing to write those characters themselves in 'set -x',
'export -p' and the like.
The implementation attempts to comply to the proposal for the next issue of
the POSIX specification. Because this construct is not in POSIX.1-2008,
using it in scripts intended to be portable is unwise.
Matching the minimal locale support in the rest of sh, the \u and \U
sequences are currently not useful.
Exp-run done by: pav (with some other sh(1) changes)
Diffstat (limited to 'bin/sh/sh.1')
-rw-r--r-- | bin/sh/sh.1 | 73 |
1 files changed, 71 insertions, 2 deletions
diff --git a/bin/sh/sh.1 b/bin/sh/sh.1 index e9f34fb..e240d7d 100644 --- a/bin/sh/sh.1 +++ b/bin/sh/sh.1 @@ -32,7 +32,7 @@ .\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95 .\" $FreeBSD$ .\" -.Dd March 20, 2011 +.Dd May 5, 2011 .Dt SH 1 .Os .Sh NAME @@ -396,13 +396,82 @@ Quoting is used to remove the special meaning of certain characters or words to the shell, such as operators, whitespace, keywords, or alias names. .Pp -There are three types of quoting: matched single quotes, +There are four types of quoting: matched single quotes, +dollar-single quotes, matched double quotes, and backslash. .Bl -tag -width indent .It Single Quotes Enclosing characters in single quotes preserves the literal meaning of all the characters (except single quotes, making it impossible to put single-quotes in a single-quoted string). +.It Dollar-Single Quotes +Enclosing characters between +.Li $' +and +.Li ' +preserves the literal meaning of all characters +except backslashes and single quotes. +A backslash introduces a C-style escape sequence: +.Bl -tag -width xUnnnnnnnn +.It \ea +Alert (ring the terminal bell) +.It \eb +Backspace +.It \ec Ns Ar c +The control character denoted by +.Li ^ Ns Ar c +in +.Xr stty 1 . +If +.Ar c +is a backslash, it must be doubled. +.It \ee +The ESC character +.Tn ( ASCII +0x1b) +.It \ef +Formfeed +.It \en +Newline +.It \er +Carriage return +.It \et +Horizontal tab +.It \ev +Vertical tab +.It \e\e +Literal backslash +.It \e\&' +Literal single-quote +.It \e\&" +Literal double-quote +.It \e Ns Ar nnn +The byte whose octal value is +.Ar nnn +(one to three digits) +.It \ex Ns Ar nn +The byte whose hexadecimal value is +.Ar nn +(one or more digits only the last two of which are used) +.It \eu Ns Ar nnnn +The Unicode code point +.Ar nnnn +(four hexadecimal digits) +.It \eU Ns Ar nnnnnnnn +The Unicode code point +.Ar nnnnnnnn +(eight hexadecimal digits) +.El +.Pp +The sequences for Unicode code points currently only provide useful results +for values below 128. +They reject code point 0 and UTF-16 surrogates. +.Pp +If an escape sequence would produce a byte with value 0, +that byte and the rest of the string until the matching single-quote +are ignored. +.Pp +Any other string starting with a backslash is an error. .It Double Quotes Enclosing characters within double quotes preserves the literal meaning of all characters except dollar sign |