If you are evaling perl users are uploading, then you should be able to double check the code that is being uploaded for anything you want -- including the use of $', $`, and/or $&. You could take a friendly approch (i.e. match $content =~ m/\$'/) and spit out a warning, or be a little more beligerent (exit 1 if ($content =~ m/\$'/)</code>). Of course, couldn't you put the file in a seperate file and run that as a seperate process? That would allow you to give users the power of $' with none of the problems for you.