It looks like your making one long string in $rank, the equivalent of:$rank .= " " . $key; I'm guessing that your array has one element with one long string in it, so it looks like it's not sorted.

If you just want to get a sorted list of the keys, you can do:

@sorted = sort { $b <=> $a } keys %rank;
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Notice you don't have to do a reverse, you can just change the sense of the comparison.