Answering the first question first, you do indeed have two processes; that's what the | does in the open. See doc:perlopentut.

I'm not sure what want with the second one. If you mean that you want to stop after a specified amount of time, then you could just use alarm() to set a timer for the desired amount of time and exit the loop at that point. Like (untested): 


my $done = 0;
local $SIG{ALRM} = sub { $done = 1; };
alarm 10; # or whatever
while (not $done and $output = <STDIN>) {
  print $output; # don't need newline as it's there already
}

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In reply to Re: capture output of tcpdump and PID by thargas
in thread capture output of tcpdump and PID by mike928

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