It'd be nice if you gave us what you had tried. It really does help. Anyway ... Off the top of my head, untested: 

FORK:
{
 if (my $child = fork())
 {
   print "Child process ID: $child\n";
 }
 elsif (not defined $child)
 {
   # failed to fork.
   next FORK;
 }
 else
 {
   # child.
   open(STDOUT, '>somefile);
   close(STDIN); # just good practice for background procs
   exec($program, @program_args);
 }
}

[download]
Update: Fixed the off-by-everything error as noted by Eimi Metamorphoumai - thanks!

In reply to Re: Doing a system command and getting the pid by Tanktalus
in thread Doing a system command and getting the pid by bobhussey

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