Perl5 リファレンス

       kill SIGNAL, LIST
               Sends a signal to a list of processes.  Returns
               the number of processes successfully signaled
               (which is not necessarily the same as the number
               actually killed).

                   $cnt = kill 1, $child1, $child2;
                   kill 9, @goners;

               If SIGNAL is zero, no signal is sent to the
               process.  This is a useful way to check that the
               process is alive and hasn't changed its UID.  See
               the perlport manpage for notes on the portability
               of this construct.

               Unlike in the shell, if SIGNAL is negative, it
               kills process groups instead of processes.  (On
               System V, a negative PROCESS number will also kill
               process groups, but that's not portable.)  That
               means you usually want to use positive not
               negative signals.  You may also use a signal name
               in quotes.  See the Signals entry in the perlipc
               manpage for details.