[bug-diffutils] bug#29139: add --include for recursive searches

[Kevin Hunter Kesling]

Hello List,

I've been annoyed and confused when I'm on autopilot and attempting to 
recursively compare directory trees.  I've become accustomed to Grep's 
--include functionality, and have more than a few times been surprised 
(to the tune of "What? Unrecognized option??") that diff does not have 
it.  Well, with the attached patch, it now does.

Thanks to diff and grep both using gnulib, and the expressiveness of 
add_exclude(), this was a much easier change that I was expecting when I 
embarked on this a couple of hours ago.

Further, in the past hour since implementing it, this patch has already 
saved me a ton of time (no thanks to an unfortunately slow VPN setup and 
other beleaguered business requirements).

Use is exactly like with grep.  For example:

    $ diff --recursive --brief -w --include="*.c" --include="*.h"  \
        dir1/   \
        dir2/

Would this be of use to the community?

Thanks,

Kevin

diff-Add-include-command-line-option.patch
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