sub compare_sites {
  my($old, $new) = @_;
  if (-M $new > -M $old) {
    ($old, $new) = ($new, $old);
  }

  open(OLD, $old) or die "Can't open $old: $!\n";
  open(NEW, $new) or die "Can't open $new: $!\n";

  my(%old, %new);

  while (<OLD>) {
    chomp;
    $old{$_} = 1;
  }

  while (<NEW>) {
    chomp;
    $new{$_} = 1;
  }

  close(OLD);
  close(NEW);

  my @old = keys %old;

  delete @old{keys %new};
  delete @new{@old};

  for (sort keys %old) {
    print "$_ went down overnight.\n";
  }
  for (sort keys %new) {
    print "$_ came up overnight.\n";
  }
}