Re: feature request: tail -H

[Николай Волосатов]

Hi,
I've made this changes as part of homework and created pull-request in main 
repository on github accidentally. Sorry for that. But if it could be useful 
for someone I'll be happy.

Best regards,
Nikolay Volosatov

16.11.2015, 17:27, "Pádraig Brady" <address@hidden>:
> On 01/10/15 17:07, Pádraig Brady wrote:
>>  On 30/09/15 12:45, Stephen Shirley wrote:
>>>  Hi,
>>>  Here's the scenario: you're in a directory of updating log files
>>>  (could be /var/log), and you want to watch all files for specific
>>>  keywords. For a single file, "tail -F file | grep keyword" is
>>>  sufficient, but if you want to watch multiple files, "tail -F file1
>>>  file2 file3 | grep keyword" is much less helpful because you have no
>>>  way of knowing which log file the matching text is from.
>>>
>>>  My suggestion is to add a -H flag (convention taken from grep -H aka
>>>  --with-filename) to tail. With -H specified, tail would no longer
>>>  print out headers before file contents, it would instead prefix the
>>>  line with the file name. With this, "tail -HF file1 file2 file3 | grep
>>>  keyword" is useful, because you get the filename included in the
>>>  matching lines.
>>>
>>>  The workaround i've come up with in the meantime is:
>>>
>>>    tail -F "$@" | awk '/^$/ {next} /^==>/ {prefix=$2; next} {print
>>>  prefix ": " $0}'
>>>
>>>  but it's a bit of a hack; there's no way to be sure that a header
>>>  string is actually a header, and not part of the file contents.
>>
>>  I like that. It would be similar to the grep option: -H, --with-filename
>>
>>  You could do it with something like:
>>
>>    $ tail -f .bashrc .vimrc | grep --line-buffered -e'^==> .* <==$' -e 'gco'
>>    ==> .bashrc <==
>>    alias gco='git checkout'
>>    ==> .vimrc <==
>>
>>  However that would impact counting, and show redundant headers.
>
> I was going to look at this this evening, and coincidentally
> just noticed this pull request for a similar feature:
> https://github.com/coreutils/coreutils/pull/4
>
> Now that also incorporates timestamping and coloring,
> neither of which is warranted I think, as they
> can be added in more general manner outside of tail.
>
> For example the timestamping case was discussed recently at:
> http://lists.gnu.org/archive/html/coreutils/2015-11/msg00003.html
>
> grep has coloring internally as it provides functionality
> not possible outside, by coloring the extent of the match etc.,
> and the file name coloring is just an ancillary albeit useful extension.
>
> cheers,
> Pádraig.