# Check if the program is running or died unexpectedly
if (-e $PIDFile) {
  print "Error: $0 is still running.";
  # Here you can gracefully remove the process or just kill
  # it using a SIGNAL or kill this process and let the
  # original one run
} else {
  open (PID, '>',$PIDFile);
  print PID $$;
  close (PID);
}