You have quote-itis. First, you don't need to quote simple strings as hash keys:

$dir = $in{sub_dir};
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Second, placing variables inside single quotes does not expand them to their value. And you don't need to use double quotes either:

rmtree([$dir_location, $dir], 1, 1);
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But I have an odd feeling you mean to do:

rmtree([ "$dir_location/$dir" ], 1, 1);
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japhy -- Perl and Regex Hacker