How to catch that pid?

mudMonk has asked for the wisdom of the Perl Monks concerning the following question:

My need: I want to run an executable and kill it when I'm done with it. (OS is linux)

My problem: I realized open3 returns the pid only at closure.

My Question: How to run a system process and capture its pid while it's still running?

I've written this mangled piece of code as a patch for now, but I'm sure there are much better answers out there.

Your thoughts?

sub pidKill {
#-----------------------------------------------------------
#  USE:        kills the last process seen in output of
#              ps.
#              (This begs to kill the wrong program.)
#  ARGUMENTS:  $string containing program, arguments, and possibly a s
+udo in front.
#  RETURN:     none
#-----------------------------------------------------------
   my $program = shift;
   my (@output,$line);
   if ($program =~ /^sudo /) { $program=$'; }
   if ($program =~ / /)      { $program=$`; }
   while ($program =~ /\//)  { $program=$'; }
   @output = `ps -eo "%p %c" | grep $program`;
   foreach (@output) { $line = $_; }
   trim($line); # like chomp but can strip leading spaces too.
   $line=~/ /;   $line = $`; #should have just the prog now.
   kill 'KILL' , $line;
}
[download]

Comment on How to catch that pid? Download Code

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Re: How to catch that pid? by ikegami (Patriarch) on Jan 20, 2012 at 22:53 UTC
My problem: I realized open3 returns the pid only at closure. If "at closure" means when the child exits, that's wrong. `open3` returns the childs pid, and `open3` returns as soon as the child is launched. `use feature qw( say ); use IPC::Open3 qw( open3 ); open(local TO_CHLD, '<', '/dev/null') or die $!; my $pid = open3( '<TO_CHLD', local FR_CHLD, '>STDERR', 'perl', '-E', 'sleep 2; say $$;' ); say time, ": ", $pid; while (<FR_CHLD>) { print time, ": Perl said: $_"; } waitpid($pid, 0);` [download] `1327100100: 27601 1327100102: Perl said: 27601` [download]	[reply] [d/l] [select]
Re: How to catch that pid? by JavaFan (Canon) on Jan 20, 2012 at 22:35 UTC
Well, the usual way is to use `fork`, which will give you the PID, and then an `exec` in the child. In fact, assuming a Unix or Unix like platform, this will be happening being the scenes regardless how to start a different process.	[reply] [d/l] [select]
Re: How to catch that pid? by BrowserUk (Patriarch) on Jan 20, 2012 at 22:30 UTC
My problem: I realized open3 returns the pid only at closure. If you add an `&` to the end of your command, it will be run asynchronously and open3 will be able to return the pid to you immediately. You would need to add a shell into the mix though. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply] [d/l]
Re: How to catch that pid? by Anonymous Monk on Jan 21, 2012 at 04:22 UTC
Use Proc::Background	[reply]


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