my @pids;
my $pid;
if ($pid = fork()) {
  # Parent process
    push(@pids, $pid);
} else {
  # Child process
  exec('md5', $IdocFileName, $IdocMd5FileName);
  exit; # This should never be reached.
}
...
# Clean up the children later...
foreach $pid (@pids) {
  waitpid($pid);
}