in reply to Emulating command line pipe

Don't use system - if you just open a pipe from tac to yourself, you have full control. 
my $tac_pid = open my $fh, "tac $logfile |";
while (<$fh>) {
    last if /$match/;
}
kill 13, $tac_pid; # SIGPIPE
close $fh;

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But even so tac might be reading more than it should needed, since there's buffering on both sides of the pipe (and yes, I guess closing the filehandle $fh sends a SIGPIPE to tac... :-)

--shmem 

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

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Re^2: Emulating command line pipe
by davistv (Acolyte) on Aug 31, 2007 at 17:08 UTC
    Thank you, shmem. Unfortunately once run as a cgi the process is no longer killed upon a match, I'm not sure why. I think this might be an issue with apache, but I'm not certain.

    Thank You,
    Troy
[reply]
      AFAIK grep -m 1 exiting causes the OS to send a SIGPIPE to tac upon grep exit... hmm. Could it be that SIGPIPE is masked somewhere in mod_perl, ? is that masking propagated to the child? Is it even possible to mask a signal for a process group? Now that's something I don't know, you got me there :-)

      If that's the case - i.e. if SIGPIPE is masked - try my solution (which doesn't involve grep) and kill off tac with another signal (15 or, if it's renitent, 9 - SIGKILL).

      --shmem 

      _($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}
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[d/l]
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        That was it, changed the signal to 9 and the script now executes in about 10 seconds. Thanks!

        Cheers,
        Troy
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