my (%values, $key);
foreach my $value ( split /[&;]/, $query_string ) {
    my ($name, $data) = split /=/, $value;
    if ( lc($name) eq 'o' ) {
        $key = $data;
        $values{$key} = undef 
            unless exists $values{$key};
    } elsif ( lc($name) eq 'd' and defined $key ) {
        # anything you need to do to $data happens here
        if ( ref $values{$key} eq 'ARRAY' ) {
            push @{$values{$key}}, $data;
        } elsif ( defined $values{$key} ) {
            $values{$key} = [ $values{$key}, $data ];
        } else {
            $values{$key} = $data;
        }
    }
}

##</code><code>##

    push @{$values{$key}}, $data;