From Home|Services|WWW click on the pencil next to the mime type for the cgi extension and add the pl extension so that the extension now reads:

Extension: cgi pl
MIME Type: application/x-httpd-cgi

Note: That's a space between cgi and pl.

Then click on Store then Commit and commit your changes.

As always, the .pl file will need to have permissions set so that the web server can run the program.
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