I am using File::Copy copy because some files have all kinds of quotes and so on which make backticks, system, etc awkward. I guess I could have escaped them, but I went this way instead ... that's what modules are for, right?

What's awkward about

    system "cp", 'tmp.mp3', $target and die;
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? It doesn't matter how many quotes $target has, as there's nothing that will be interpreting the quotes.

There may be reasons to use File::Copy, but "quotes in file names" isn't one of them.