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bug#36148: inconsistent behaviour with anchored regex containing back-re
From: |
g1pi |
Subject: |
bug#36148: inconsistent behaviour with anchored regex containing back-references |
Date: |
Sun, 9 Jun 2019 10:00:24 +0200 |
User-agent: |
NeoMutt/20170113 (1.7.2) |
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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