How do I recursively count file sizes in a script that works under both Windows and Linux?

[FiReWaLL]

$directory = '/thedir/thatiwantto/count';


print "\n\n";
print CountSize($directory);
print "\n\n";

sub CountSize {
    my ($directory) = $_[0];
    my ($ask, $filesize, $item, $size, @raiz);

    @raiz = glob("$directory/*.*") || warn();
    
    foreach $item (@raiz) {
        $ask = -d $item;
        if ($ask) {
            $size += &CountSize($item);
        } else {
            $size += -s $item;
        }
    }
    return($size);
}

It should return the total size of all the tree. In Windows, it works, but in Linux, it doesn't. It returns only the current directory file sizes. What should I do?

Originally posted as a Categorized Question.