$term = 0;
$SIG{TERM} = sub { $term = 1; };

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

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

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

  # TERM has arrived, forward it to child and exit
  if ($term) { kill('TERM', $pid); exit(0); }

  # check the child again after 1 second
  sleep(1);
}