GNU bug report logs - #47001
Feature request: give a meaning to -A/-B/-C with -o

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

From: Gregory Heytings <gregory <at> heytings.org>
To: bug-grep <at> gnu.org
Subject: Feature request: give a meaning to -A/-B/-C with -o
Date: 2021年3月08日 08:21:27 +0000

Hi list,
Grep gives no meaning to the -A/-B/-C flags when they are used together 
with the -o flag (and prints a warning when they are used together).
I suggest to give them a specific meaning when the -o flag is used, namely 
to print NUM _characters_ of trailing/leading/output context around the 
match.
Currently this behavior can be obtained with "grep -oE 
'.{0,A}expose_frame.{0,B}'", where A and B are the number of leading and 
trailing context characters, but it is not efficient, and can become very 
inefficient for "large" values of A and B (say, 40).
Thanks,
Gregory

Message #8 received at 47001 <at> debbugs.gnu.org (full text, mbox):

From: Gregory Heytings <gregory <at> heytings.org>
To: 47001 <at> debbugs.gnu.org
Subject: Re: bug#47001: Feature request: give a meaning to -A/-B/-C with -o
Date: 2021年3月08日 17:12:38 +0000

Two further comments:
>
> Grep gives no meaning to the -A/-B/-C flags when they are used together 
> with the -o flag (and prints a warning when they are used together).
>
Both the manual and the man page indicate that "a warning is given" when 
these options are used together, but what actually happens is that a group 
separator is printed at apparently random places.
>
> I suggest to give them a specific meaning when the -o flag is used, 
> namely to print NUM _characters_ of trailing/leading/output context 
> around the match.
>
> Currently this behavior can be obtained with "grep -oE 
> '.{0,A}expose_frame.{0,B}'", where A and B are the number of leading and 
> trailing context characters, but it is not efficient, and can become 
> very inefficient for "large" values of A and B (say, 40).
>
Of course I meant "grep -oE '.{0,A}PATTERN.{0,B}'.
The "very inefficient" case happens in particular for very long lines:
for i in $(seq 1 10)
do
 printf %100000s | tr ' ' 'a'
 printf foobar
 printf %100000s | tr ' ' 'a'
done | grep -oE '.{0,40}foobar.{0,40}'

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