# waitpid($pid,WNOHANG) returns 0 if the child process
# exists and has not terminated

$SIG{TERM} = sub { waitpid($pid,WNOHANG) || kill('TERM', $pid); exit(0); }

# waitpid loop

for (;;) {
  $p = waitpid($pid, 0);

  # where did the child disappear?
  if ($p == -1) { exit(1); } 

  # child has terminated
  if ($p == $pid && (WIFEXITED($?) || WIFSIGNALED($?))) {
    exit($?>>8);
  }

}