2018-05-03 15:54:58 +0000, Austin Group Bug Tracker:
[...]
> On page 2492 line 80144 section awk, add two new rows to the table:<pre>
> \., \[, \(, \*, \+, | A <backslash> character followed by a character | In
> the lexical token <b>ERE</b>, the sequence
> \?, \{, \|, \^, \$ | that has a special meaning in EREs (see |
> shall represent itself. Otherwise undefined.
> | [xref to XBD 9.4.3]), other than <backslash>. |
> --------------------+-------------------------------------------------+-----------------------------------------------------
> \\ | Two <backslash> characters. | In
> the lexical token <b>ERE</b>, the sequence shall
> | |
> represent itself. In the lexical token <b>STRING</b>,
> | | it
> shall represent a single <backslash>.
> </pre>
[...]
Thanks.
Does that mean that:
awk '/[\]]/'
is to match on "\]" and not on "]" (like for grep -E '[\]]')?
In practice not many implementation do. The only ones I found
that did were busybox awk and Solaris /usr/xpg4/bin/awk.
mawk, gawk, bwk's awk, Solaris nawk, FreeBSD awk all output:
$ printf '%s\n' '\]' ']' | awk '/[\]]/'
\]
]
In practice, one does need to double the \ inside bracket
expressions for it not to be treated specially in many regexp
and wildcard engines. That's the case of several shells
(including certified ones) for
var='[\\]foo]'; case x in $var); esac
and of many REs including the modern de-facto standard that PCRE
has become.
I think POSIX should acknowledge that generally in the regular
expression syntax.
--
Stephane
