$SIG{CHLD} = sub {print("SIGCHLD\n")};

exit unless $pid = fork;
sleep 1;
system "ps -p $pid";
waitpid $pid, 0;
system "ps -p $pid";
__END__
SIGCHLD
  PID TTY          TIME CMD
29260 pts/32   00:00:00 perl <defunct>
SIGCHLD
  PID TTY          TIME CMD
SIGCHLD