GNU bug report logs - #38725
Regexp bug

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

From: Chewbaka Roskov <akem3210 <at> gmail.com>
To: bug-sed <at> gnu.org
Subject: Regexp bug
Date: Mon, 23 Dec 2019 23:09:28 +0100

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

Hello,

---------------------------------------------------------------------------
akem <at> akem-HP:~$ sed --version
sed (GNU sed) 4.4
Copyright (C) 2017 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html
>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Jay Fenlason, Tom Lord, Ken Pizzini,
and Paolo Bonzini.
GNU sed home page: <http://www.gnu.org/software/sed/>.
General help using GNU software: <http://www.gnu.org/gethelp/>.
E-mail bug reports to: <bug-sed <at> gnu.org>.
---------------------------------------------------------------------------

Regular expression bug:

akem <at> akem-HP:~$ echo '112233' | sed 's/2*//'  ### DOESN'T WORK
112233
akem <at> akem-HP:~$ echo '112233' | sed 's/1*//'  ### THIS ONE WORK
2233
akem <at> akem-HP:~$ echo 'ee112233' | sed 's/1*//'  ### BUT THIS ONE DOES NOT
ee112233

---------------------------------------------------------------------------

Best regards.

[Message part 2 (text/html, inline)]

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

From: Davide Brini <dave_br <at> gmx.com>
To: bug-sed <at> gnu.org
Subject: Re: bug#38725: Regexp bug
Date: Tue, 24 Dec 2019 18:30:14 +0100

On Mon, 23 Dec 2019 23:09:28 +0100, Chewbaka Roskov <akem3210 <at> gmail.com>
wrote:

> akem <at> akem-HP:~$ echo '112233' | sed 's/2*//'  ### DOESN'T WORK
> 112233

You're asking for "zero or more twos". At the beginning of the string (and
between each pair of characters) there is indeed a zero-length match for
your regexp, which sed duly replaces with nothing as you asked. Had you
replaced with something or used the /g switch to the "s" command, you'd
have seen it. For example:

$ echo '112233' | sed 's/2*//g'
1133
$ echo '112233' | sed 's/2*/XXX/'
XXX112233

# Blatant test case

$ echo 'abc' | sed 's/2*/XXX/g'
XXXaXXXbXXXcXXX


> akem <at> akem-HP:~$ echo '112233' | sed 's/1*//'  ### THIS ONE WORK
> 2233

In this case 1* matches at the beginning of the string as before, but it's
allowed to match more than zero characters, so the "11" (the match for 1*)
is replaced with nothing.

> akem <at> akem-HP:~$ echo 'ee112233' | sed 's/1*//'  ### BUT THIS ONE DOES NOT
> ee112233

Same as first case.

--
D.

Message #11 received at 38725 <at> debbugs.gnu.org (full text, mbox):

From: Assaf Gordon <assafgordon <at> gmail.com>
To: Davide Brini <dave_br <at> gmx.com>, 38725 <at> debbugs.gnu.org
Subject: Re: bug#38725: Regexp bug
Date: Tue, 24 Dec 2019 14:34:37 -0700

tag 38725 notabug
close 38725
stop

Hello,

On 2019-12-24 10:30 a.m., Davide Brini wrote:
> On Mon, 23 Dec 2019 23:09:28 +0100, Chewbaka Roskov <akem3210 <at> gmail.com>
> wrote:
> 
>> akem <at> akem-HP:~$ echo '112233' | sed 's/2*//'  ### DOESN'T WORK
>> 112233
> 
> You're asking for "zero or more twos". At the beginning of the string (and
> between each pair of characters) there is indeed a zero-length match for
> your regexp, which sed duly replaces with nothing as you asked. Had you
> replaced with something or used the /g switch to the "s" command, you'd
> have seen it. For example:
> 
> $ echo '112233' | sed 's/2*//g'
> 1133
> $ echo '112233' | sed 's/2*/XXX/'
> XXX112233

Thank you Davide for the clear explanation.

I'm closing this as "not a bug", but discussion can continue
by replying to this thread.

regards,
 -assaf

Message #18 received at 38725 <at> debbugs.gnu.org (full text, mbox):

From: Chewbaka Roskov <akem3210 <at> gmail.com>
To: 38725 <at> debbugs.gnu.org
Subject: Thank you for detailled explanation.
Date: Fri, 27 Dec 2019 23:01:22 +0100

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

Thank you very much, sorry for misreporting this as a bug.

[Message part 2 (text/html, inline)]

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