All of these solutions seem to have a really serious problem: you're passing the same file tree over-and-over again, using an external program (find) to collect data that's easily accessible to perl.

My interperter is being updated, so here's the start of a solution for 1-pass. A structure is built that just has to be dumped to disk however you want.

Untested, of course.

use File::Find;
sub wanted {
        $a=$File::Find::name;
        return if -l $a;   # Necessary?
        $o=(stat($a))[4];
        push( @{$catalog{$o}}, $a);
}
find(\&wanted, "/home/ul");
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