if (defined($hash{$key}) {
    $hash{$key} ++;
  } else {
    $hash{$key} = 1;
  }

##</code><code>##

    $hash{$key}++;

##</code><code>##

  %hash = ("www.yahoo.com", 10, "www.google.com", 2000);
  foreach (keys %hash) {
    $rev_hash{$hash{$_}} = $_;
  }
  foreach (sort keys %rev_hash) {
    print "$rev_hash{$_} appears: $_ time(s)\n";
  }

##</code><code>##

  %hash = (
     www.yahoo.com => 10,
     www.google.com => 2000,
  );

  for ( sort { $hash{$a} <=> $hash{$b} } keys %hash )
  {
    print "$_ appears: $hash{$_} time(s)\n";
  }