How do I sort a hash (optionally by value instead of key)?

    @keys = sort keys %hash;    # sorted by key
    @keys = sort {
                    $hash{$a} cmp $hash{$b}
            } keys %hash;       # and by value

Here we'll do a reverse numeric sort by value, and if two keys are identical, sort by length of key, and if that fails, by straight ASCII comparison of the keys (well, possibly modified by your locale -- see the perllocale manpage).

    @keys = sort {
                $hash{$b} <=> $hash{$a}
                          ||
                length($b) <=> length($a)
                          ||
                      $a cmp $b
    } keys %hash;