Points for pointing out that `s/// for @array` is 50% faster than `grep {} @array`.

You could also do all three s/// at the same time:

    s/user::/USER:$o:/, s/group::/GROUP:$g:/, s/other::/OTHER::/ for @
+A;
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For the third one, it comes at the prices of understanding the intention of the line code. But if I just don't use newlines, it might be better.

Another way to do that which may be better:

    $P{$k} =~ tr/ \n\r\t\f/ /s; # remove newlines
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