# Turns numerical return codes into text.  See perlvar.
sub get_system_error {
  my $code = shift;
  print "Code: $code\n";
  unless ($code < 2**8) {
    $code >>= 8;
  }
  local $! = $code;
  return "$!";
}

##</code><code>##

if (0 < $?) {
  my $sys_msg = get_system_error($?);
  die "'$cmd' failed. ret code $?.  (Guess: '$sys_msg'?)";
}