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

[Richard Retanubun <richardretanubun@ruggedcom.com>]

On 24/01/12 03:17 PM, Richard Retanubun wrote:
> 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 --
Sorry, one more question to clarify, which "recent dash versions" have the optimization?

Debian changelog from wheezy (0.5.7-2) says this:

0005-SHELL-Disable-sh-c-...diff: back out the optimization
that makes dash -c "script" avoid a fork().  It caused
several packages to fail to build from source (thx Stéphane Glondu, closes: #642922).

So it used to, but does not currently?

-- Richard