GNU logs - #36148, boring messages

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Subject: bug#36148: inconsistent behaviour with anchored regex containing back-references
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Date: Sun, 9 Jun 2019 10:00:24 +0200
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There seems to be a problem with beginning/end-of-line anchors in regex
containing back-references:

$ grep -V | head -1
grep (GNU grep) 3.1

$ cat words
ana
deed
ill
stats

Using -x to match whole line works:

$ egrep -x '(.?)(.?).?\2\1' words 
ana
deed
stats

Using explicit anchors emits false positives:

$ egrep   '^(.?)(.?).?\2\1$' words 
ana
deed
ill	<<<
stats

On the other hand, colouring the output shows that grep somewhat knows its
mistake:

$ egrep --color '^(.?)(.?).?\2\1$' words 
ana	(coloured)
deed	(coloured)
ill
stats	(coloured)

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From: help-debbugs@HIDDEN (GNU bug Tracking System)
To: g1pi@HIDDEN
Subject: bug#36148: Acknowledgement (inconsistent behaviour with anchored
 regex containing back-references)
Message-ID: <handler.36148.B.15600941636275.ack <at> debbugs.gnu.org>
References: <20190609080024.sywtiytvlajpd4ko@moon>
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Date: Sun, 09 Jun 2019 15:30:02 +0000

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From: Paul Eggert <eggert@HIDDEN>
Subject: 26864 and 36148 are the same bug
Organization: UCLA Computer Science Department
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merge 36148 26864

Message sent to bug-grep@HIDDEN:

Subject: bug#36148: inconsistent behaviour with anchored regex containing back-references
References: <20190609080024.sywtiytvlajpd4ko@moon>
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From: Paul Eggert <eggert@HIDDEN>
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Date: Thu, 2 Jan 2020 01:37:20 -0800
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Yes, back-references don't work very well. This looks to be the same bug as
Bug#26864 <https://bugs.gnu.org/26864> so I have merged the two bug reports.

Last modified: Thu, 2 Jan 2020 09:45:02 UTC

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