Perl since 5.8.something has had the option of perturbing the hash function, so it is different from run to run. You can also set the set to a given value in or

Perl since 5.8.something has had the option of perturbing the hash function, so it is different from run to run. You can also set the set to a given value in order to lock in the sequence. In any case, it is not ordered. If you want that, you have to explicitly sort the keys of the hash.