Re: /bin/dash -c != /bin/bash -c with pgrep

[Richard Retanubun <richardretanubun@ruggedcom.com>]

On 24/01/12 02:43 PM, Jonathan Nieder wrote:
> Hi Richard,
>
> Richard Retanubun wrote:
>
>> /bin/dash -c "pgrep -f /usr/sbin/atftpd"; echo $?
>> -vs-
>> /bin/bash -c "pgrep -f /usr/sbin/atftpd"; echo $?
>>
>> The dash version returns the PID of the grep itself and thus always succeeds.
>> The bash version works as expected.
>
> As the pgrep(1) manual explains, the running pgrep or pkill process
> will never report itself as a match.  However, when running pgrep
> through dash, it reports the process id of the shell executing pgrep,
> while the bash version and recent dash versions optimize "sh -c
> 'single command'" to
>
> 	sh -c 'exec pgrep -f /usr/sbin/atftpd'
>
> so there is no shell process left to report.
>
> If that "exec" is specified explicitly, the result is the same in both
> shells.
>
> Hope that helps,
> Jonathan
It sure does, thanks a lot Jonathan.

As an addendum, I find using "pgrep -x atftpd" in this case also yields the
expected output in both shell.

Thanks for your time.

-- RR --