# note passing your sub $a and $b
foreach my $id (sort { mysort($direction,$a,$b) } keys %hash) {
  print "$id - $hash{$id}{$orderby}\n";
} # end-foreach

sub mysort {
    my ($direction, $_a, $_b) = @_;
    my $result =  
        $hash{$_a}{$orderby} <=> $hash{$_b}{$orderby}
        || $hash{$_a}{$orderby} cmp $hash{$_b}{$orderby};
    
    # default to ascending, but if the dir is 'DESC', we
    # return the *opposite* answer
    return ($direction eq 'DESC') ? -($result) : $result;
}