bug#66434: grep recently shows the filename with -o , but it shouldn't.

[Gary Johnson]

On 2023-10-10, Joerg M. Sigle wrote:
> Hello GNU grep team
> 
> I have grep (GNU grep) 3.6 on a Debian / Devuan Linux system.
> 
> Recently I noticed that when using the -o switch, grep also shows
> the filename for each hit in front of the desired output, and
> a ":" as separator.
> IIRC this was not the case in previous versions of grep [but
> please correct me if I'm wrong here].
> 
> In any case, the filename: is NOT shown before matching content
> when the -o switch is not used.

This depends on the number of files being searched and on the
presence of the -h or -H switch.  It should not be affected by the
-o switch.  I tested the few versions I have on hand, 3.4, 3.7 and
3.11, and they all behave according to the man page with respect to
the -o flag and the number of files searched.

> According to the manual, the -o switch should only limit output to
> matching parts, and NOT ADDITIONALLY activate the output of
> filename:
> 
> -o, --only-matching
>       Print only the matched (non-empty) parts of a matching line,
>       with each such part on a separate output line.
> 
> 
> N.B.:
> Showing the filename ONLY instead of matching lines/only matching
> part) IS already controlled with the -l switch.
> So a different switch would be needed to show the filename IN
> ADDITION to the output of -o.
> I think, somebody thought they'd do something beneficial by
> showing the filename in front of the output of -o, but I'm afraid
> they are not.
> And I'm also afraid that this needs some workaround to remove the
> filename again for many applications of grep,
> so changing back to the expected behaviour might cause trouble
> again, of course.
> 
> Example:
> 
> $ grep  -o PV1.... *.hl7
> 
> Currently produced output (supposedly wrong):
> 
> PAT_20231010_112021_010166.hl7:PV1|1|O
> PAT_20231010_112021_010167.hl7:PV1|1|O
> PAT_20231010_112420_010168.hl7:PV1|1|I
> PAT_20231010_112421_010169.hl7:PV1|1|I
> PAT_20231010_112421_010170.hl7:PV1|1|I
> ...
> 
> Desired output (supposedly right):
> PV1|1|O
> PV1|1|O
> PV1|1|I
> PV1|1|I
> PV1|1|I
> ...

Grep is behaving correctly, according to this part of the man page:

    -H, --with-filename
           Print the file name for each match.  This is the default
           when there is more than one file to search.  This is
           a GNU extension.

    -h, --no-filename
           Suppress the prefixing of file names on output.  This is
           the default when there is only one file (or only standard
           input) to search.

Regards,
Gary