There's a typo in the code you provided.

sub walk_hash {
    my ($h1, $h2) = shift;
    foreach my $key (keys %$h) {       # I presume you mean %$h1 here?
        if( ref $h->{$key}) {          # And $h1->... here?
            walk_hash( $h->{$key} );   # and here?
        }
        else {
            print $h->{$key};          # and here as well?
        }
    }
}
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Other than that, I suggest you check the modules Tux pointed at, above.