GNU bug report logs - #75806
Trailing spaces; pattern "\s" before "[[:cntrl:]]" faulty

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From: Peter White <peter.white <at> posteo.net>
To: 75806 <at> debbugs.gnu.org
Subject: bug#75806: Trailing spaces; pattern "\s" before "[[:cntrl:]]" faulty
Date: Fri, 24 Jan 2025 19:26:00 +0000

On Fri, Jan 24, 2025 at 01:27:13PM +0000, Andreas BROCKMANN via Bug reports for GNU grep wrote:
> Hi,
> 
> The 1st command below correctly reports trailing spaces, for Unix and Windows format files.
> The 2nd one incorrectly reports all lines.
> 
>   grep -sHn -i " [[:cntrl:]]*$" *.vhd
>   grep -sHn -i "\s[[:cntrl:]]*$" *.vhd

As someone who just today made a similar mistake I would like to point
out that the pattern does as intended because '*' matches *zero* or more
occurrences of the preceding atom. So the second pattern matches
any line that contains a *literal* 's' followed by zero or more control
chars, which is any line because of the newline at the end which is a
control char. Since you did not ask for perl regex (-P) grep uses basic
POSIX regex instead; at least I *think* you want perl syntax given that
'\s' is only valid in PCRE, IIRC.

Also [:cntrl:] is not the correct char class for white space, why not
[:space:] or [:blank:]? Your first pattern just happens to match the
literal space in it *and* any following string of zero or more control
chars.


PW

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