Regarding the question: what does  {$playlist{$_} = 1 do: In a while(<PLAYLIST>) loop like yours, $_ contains the current record, so the statement you are wondering about sets a value of 1 in the hash for the current record. One reason I can see why this would fail is if you have trailing spaces in your input file, because e.g.'cool_song.mp3  ' is not the same as 'cool_song.mp3', which is what you will get from readdir. So this is how I would code the loop to avoid this:

while (<PLAYLIST>) {
   s/#.*//g;             #delete comments
   s/(^\s*|\s*$)//g;     #delete leading and trailing spaces
   $playlist{$_} = 1 if /\.mp3$/;
}
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To tell exactly what failed, of course, I would have to see also the input file.

Don't be discouraged, be cautious - we all deleted precious files some time or other.

pike