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

[Stefan Beller <sbeller@google.com>]

+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 <mikachu@gmail.com> wrote:
> On Mon, Nov 16, 2015 at 10:43 PM, Stefan Beller <sbeller@google.com> wrote:
>> 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.