GNU bug report logs - #27931
grep -o fails to count empty lines (Debain Bug #532541)

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

From: "Santiago R.R." <santiagorr <at> riseup.net>
To: bug-grep <at> gnu.org
Cc: 532541 <at> bugs.debian.org
Subject: grep -o fails to count empty lines (Debain Bug #532541)
Date: Thu, 3 Aug 2017 15:28:14 +0200

(Sorry if it's already filed, but I am unable to find it in the
bug archives)

Hi,

I'd like to forward this bug reported to Debian some years ago.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=532541
It still happens in 3.1.

Quoting the original report:

When grepping for empty lines in a text file, grep works correctly in
most cases:

~$ grep ^$ myfile.txt 





~$ grep -n ^$ myfile.txt 
11:
15:
19:
21:
22:

However the -o option, which is supposed to return only the matching
parts of the search, fails:

~$ grep -o ^$ myfile.txt 
~$ grep -no ^$ myfile.txt
~$ 


Thanks,

Santiago

Message #10 received at 27931-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: "Santiago R.R." <santiagorr <at> riseup.net>, 27931-done <at> debbugs.gnu.org
Cc: Greg Trounson <gregt <at> maths.otago.ac.nz>, Paolo Bonzini <bonzini <at> gnu.org>,
 Kai YU <yukai <at> nlsde.buaa.edu.cn>, 532541 <at> bugs.debian.org
Subject: Re: bug#27931: grep -o fails to count empty lines (Debain Bug #532541)
Date: Thu, 3 Aug 2017 13:16:52 -0700

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

On 08/03/2017 06:28 AM, Santiago R.R. wrote:
> the -o option, which is supposed to return only the matching
> parts of the search, fails:

It's not failing. It's behaving as documented: -o outputs only nonempty 
matches. Otherwise, commands like 'grep -o "a*"' would output a separate 
line for each byte in the input. Although this behavior for -o is 
longstanding and is documented in the manual, it's not in the grep 
--help output so that's an oversight. I installed the attached to fix 
grep --help, and am closing the bug report on the GNU side.

Users who want to match empty lines can use 'grep "^$"', which is what 
I'd expect them to do anyway (-o would be superfluous there even if it 
included empty matches).

[0001-doc-improve-o-help.patch (text/x-patch, attachment)]

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