Tip #1 from the Basic debugging checklist: use warnings

You will see a warning message

Unquoted string "i" may clash with future reserved word at ...
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You should change:

system ("rm", "-fr", $files[i]);
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to:

system ("rm", "-fr", $files[$i]);
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If you use Tip #6 from the Basic debugging checklist (B::Deparse), you will see how Perl interprets your code:

    system 'rm', '-fr', $files[0];
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