I recently gave some advice about negating the PID of process to kill its children: Re: open (to read) and kill a pipe to a pipe. According to the perldoc for kill, I was wrong. And the OP in that thread reported that doing it the way I suggested didn't work but trying per the doc did work, on Windows no less. But the "wrong" way seems to work on *nix too. Anyone know why? 

system("sleep 1234 &");
my ( $pid ) =
    qx{ pgrep -f sleep | xargs ps | grep "1234" | grep -v grep }
    =~ /(\d+)/;

print "Check me\n\tps $pid\n";

# kill 9 => $$; # Leaves sleep process alive.

# kill -9 => $$; # Kills sleep process.

kill 9 => -$$; # Also kills sleep process.

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(Updated title to include "kill.")

In reply to Kill negated PIDs v negated SIGs by Your Mother

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