Re: using find-grep in emacs

["Andreas Röhler" <andreas.roehler@easy-emacs.de>]

Am 14.05.2013 17:42, schrieb Bob Proulx:
> Peter Dyballa wrote:
>> schrieb Andreas Röhler:
>>> Because a Null -- 0 -- offers the most space to fill all that in?
>>
>> No! It's the least space to read from. No other file ends earlier.
>
> In case this issue confuses people I wanted to say a few words.  Prior
> to the addition of the grep -H option the behavior was this following.
> The grep, egrep, fgrep programs would print matching lines from files.
> If one file was searched then no file name would be printed.  If more
> than one file was searched then grep would prefix the line by the name
> of the file so that you could tell which file it came from.
>
> So the problem was how do you instruct grep to print the name of the
> file even when you were only searching one file?  The answer was to
> tell grep to search more than one file.  But, you say, I only want to
> search one file.  The answer is to search /dev/null in addition to
> whatever file you are wanting to search.  /dev/null will return end of
> file immediately.  It won't use any cpu time.  With multiple files
> being searched grep will print the file name on each line.  An elegant
> Unix solution.  That is why the grep template uses grep with /dev/null
> so that grep will print the file name so that Emacs compile mode can
> parse it.
>
> GNU grep has an extension to print file names without needing to have
> an extra null file argument.  With GNU grep you can specify the -H
> option and GNU grep will print the file name for all matches
> regardless of the number of files being searched.  Newer emacs
> versions use this option and make the assumption that you have GNU
> grep available.  (Or it might figure it out dynamically.  I don't
> know.)
>
> But the grep -H option is only available in GNU grep for the GNU
> system and BSD grep for BSD systems.  It is not available in the older
> traditional Unix systems.  It isn't in the POSIX standard.  Therefore
> using -H is non-portable.  It won't work on HP-UX or IBM AIX for example.
>
>    http://pubs.opengroup.org/onlinepubs/009695399/utilities/grep.html
>
> But if you are using Emacs then you probably have grep -H available
> too and might as well use it.
>
> The Emacs grep find templates can be customized.  See the
> grep-find-template variable in this case for example.
>
> Bob
>
>

Thanks a lot digging into, great to learn that.

Andreas