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

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Andreas BROCKMANN <andreas.brockmann <at> diehl.com>
To: "bug-grep <at> gnu.org" <bug-grep <at> gnu.org>
Cc: "cygwin <at> cygwin.com" <cygwin <at> cygwin.com>
Subject: Trailing spaces; pattern "\s" before "[[:cntrl:]]" faulty
Date: Fri, 24 Jan 2025 13:27:13 +0000

[Message part 1 (text/plain, inline)]

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

grep -V
grep (GNU grep) 3.0
Packaged by Cygwin (3.0-2)
Copyright (C) 2017 Free Software Foundation, Inc.

cmd --help
Microsoft Windows [Version 10.0.19045.5371]
(c) Microsoft Corporation. All rights reserved.

Kind Regards
Brockmann

Andreas Brockmann, Dipl.-Ing.
Hardware Engineer
Strategic Business Segment Aircraft Systems
HW & Mech. Engineering & Config. Management

phone +49 7551 891 4104
andreas.brockmann <at> diehl.com | www.diehl.com/aviation

Diehl Aerospace GmbH
Alte Nussdorfer Strasse 23 | 88662 Ueberlingen | Germany

Diehl Aerospace is a Joint Diehl Thales Company

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Message #8 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Peter White <peter.white <at> posteo.net>
To: bug-grep <at> gnu.org
Subject: Re: 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

Message #11 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Peter White <peter.white <at> posteo.net>
To: bug-grep <at> gnu.org
Subject: Re: bug#75806: Trailing spaces; pattern "\s" before "[[:cntrl:]]"
 faulty
Date: Fri, 24 Jan 2025 22:59:27 +0000

On Fri, Jan 24, 2025 at 07:26:00PM +0000, Peter White wrote:
> 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.

Turns out that last part is not true, sorry. I was going by the grep(1)
man page instead of `info grep`, which does say that '\s' is shorthand
for '[[:space:]]'. Still, the 2nd pattern is incorrect. IIUC this is
what it should look like:

	# '-i' is bogus since there is no upper/lower case whitespace
	grep --color=never -sHn '[[:blank:]][[:cntrl:]]*$'

[:blank:] is the more correct char class because '\s' matches anything
in the ASCII range 0-31 (plus <DEL>[127]) and as it so happens <CR> is
in that range. DOS files have the <CR> in front of <LF> (a.k.a. '$'),
which is why the original pattern did match *correctly*. Contrary to the
claim in the OP I could only reproduce the "false" behavior with DOS and
not UNIX files. And now I understand why '[[:cntrl:]]' is in the pattern
(sorry for my initial misunderstanding). DOS, the gift that keeps on
giving. :P

Also note the '--color=never'. I don't know how relevant this is on
Windows but on my terminal emulator (with --color=auto) the <CR> at the
end of a line in DOS files would be printed as a match and the terminal
obeyed with all the ensuing consequences, leaving empty lines without
match text. Another "gift", I guess.


PW

Message #14 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Marcus Blumhagen <marcus.blumhagen <at> posteo.de>
To: bug-grep <at> gnu.org
Subject: Re: bug#75806: Trailing spaces; pattern "\s" before "[[:cntrl:]]"
 faulty
Date: Fri, 24 Jan 2025 19:00:02 +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 - you did not ask for perl regex and thus got 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:]?

Message #19 received at 75806-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Andreas BROCKMANN <andreas.brockmann <at> diehl.com>
Cc: "cygwin <at> cygwin.com" <cygwin <at> cygwin.com>, 75806-done <at> debbugs.gnu.org
Subject: Re: bug#75806: Trailing spaces; pattern "\s" before "[[:cntrl:]]"
 faulty
Date: Sat, 25 Jan 2025 11:31:06 -0800

On 2025-01-24 05:27, Andreas BROCKMANN via Bug reports for GNU grep wrote:
> 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

I don't see a bug. The latter command is equivalent to:

   grep -Hins '[[:space:]][[:cntrl:]]*$' *.vhd

and if the input files use Microsoft CRLF format then [[:space:]] 
matches the CR at the end of every line and [[:cntrl:]]* matches the 
empty string after the CR.

Possibly you need to use Unix LF format, or use the --text option, or 
something like that.

Marking the bug as done.

Message #22 received at 75806-done <at> debbugs.gnu.org (full text, mbox):

From: Brian Inglis <Brian.Inglis <at> SystematicSW.ab.ca>
To: 75806-done <at> debbugs.gnu.org
Cc: Andreas BROCKMANN <andreas.brockmann <at> diehl.com>, cygwin <at> cygwin.com,
 Paul Eggert <eggert <at> cs.ucla.edu>
Subject: Re: bug#75806: Trailing spaces; pattern "\s" before "[[:cntrl:]]"
 faulty
Date: Sat, 25 Jan 2025 13:42:02 -0700

On 2025-01-25 12:31, Paul Eggert via Cygwin wrote:
> On 2025-01-24 05:27, Andreas BROCKMANN via Bug reports for GNU grep wrote:
>> 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
> 
> I don't see a bug. The latter command is equivalent to:
> 
>     grep -Hins '[[:space:]][[:cntrl:]]*$' *.vhd
> 
> and if the input files use Microsoft CRLF format then [[:space:]] matches the CR 
> at the end of every line and [[:cntrl:]]* matches the empty string after the CR.
> 
> Possibly you need to use Unix LF format, or use the --text option, or something 
> like that.
> 
> Marking the bug as done.

IIRC even Cygwin dropped Windows text handling in coreutils, findutils, grep, 
sed, etc. about 2018 to be consistent with other POSIX platforms.

Use d2u/dos2unix or u2d/unix2dos in pipes to convert, or equivalent, such as
tr -d '\r', sed -e 's/\r//g', awk -e '{gsub(/\r/,"")'.

Cygwin users may be able to compensate by remounting the filesystem with a 
"text" mount option -o text or the equivalent in an /etc/fstab entry, but I am 
unsure if anyone has tested using that option nowadays.

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retrancher  but when there is no more to cut
                                -- Antoine de Saint-Exupéry

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