Make that

chdir("$contentdir") or die "Couldn't chdir ..., ";
opendir THISDIR, '.' or die "Couldn't opendir ..., ";
my @submenu = readdir THISDIR or die "Nothing to readdir, ";
close THISDIR; # really need a die here too :)
[download]

Then you got lost. You tried this:

($sub1, $sub2, $sub3) = split (/\_/, $_,3);
[download]

Except that $_ wasn't set by anything yet. Your directories are in @submenu, and split only works on one scalar (at a time).

Moreover, sort is redundant on scalars:

$sub3 = sort { $b <=> $a } $sub3;
[download]

Somehow you need to pick which of the @submenu entries you want to split (or perhaps all?), and then what it is you're sorting...