How can I get the unique keys from two hashes?

First you extract the keys from the hashes into lists, then solve the "removing duplicates" problem described above. For example:

    %seen = ();
    for $element (keys(%foo), keys(%bar)) {
	$seen{$element}++;
    }
    @uniq = keys %seen;

    @uniq = keys %{{%foo,%bar}};

    %seen = ();
    while (defined ($key = each %foo)) {
        $seen{$key}++;
    }
    while (defined ($key = each %bar)) {
        $seen{$key}++;
    }
    @uniq = keys %seen;