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

[Jonathan Nieder <jrnieder@xxxxxxxxx>]

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
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