If you already know the process id(s), and own the processes, the kill builtin function might be of use.

From the doco:

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

    If SIGNAL is zero, no signal is sent to the process, but the
    kill(2) system call will check whether it's possible to send
    a signal to it (that means, to be brief, that the process is
    owned by the same user, or we are the super user).  This is
    a useful way to check that a child process is alive.