Re: [PATCH] Optimize usage of grep by passing -q

+cc Andrey Rybak, who I credit for finding the reasoning below (he
sent to me privately,
without cc'ing the list)

On Mon, Nov 16, 2015 at 4:59 PM, Mikael Magnusson [off-list ref] wrote:

On Mon, Nov 16, 2015 at 10:43 PM, Stefan Beller [off-list ref] wrote:

quoted

Instead of redirecting all grep output to /dev/null, we can just
pass in -q instead. This preserves the exit code behavior, but is faster.
As grep returns true if it finds at least one match, grep can exit promptly
after finding the first line and doesn't need to find more occurrences
which would be redirected to /dev/null anyways.

This is true for the gnu version of grep. I am not sure if all
versions of grep support this optimization. In case it is not,
we'd revert this patch.

POSIX specifies -q, so you should be fine.
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html

From http://www.gnu.org/software/grep/manual/grep.html :

-q
--quiet
--silent
Quiet; do not write anything to standard output. Exit immediately with
zero status if any match is found, even if an error was detected. Also
see the -s or --no-messages option. (-q is specified by POSIX.)
-s
--no-messages
Suppress error messages about nonexistent or unreadable files.
Portability note: unlike GNU grep, 7th Edition Unix grep did not
conform to POSIX, because it lacked -q and its -s option behaved like
GNU grep's -q option.1
USG-style grep also lacked -q but its -s option behaved like GNU
grep's. Portable shell scripts should avoid both -q and -s and should
redirect standard and error output to /dev/null instead. (-s is
specified by POSIX.)

Reading that in full, I think my patch is a bad idea.