You should have access to a cron daemon; write a separate script that compares the current time with the time the session was created for each file in the directory you store the scripts, and if it exceeds a time you designate for how long you'd expect a user to stay at your site, delete the file. Have this run every 15/30/60 minutes, or whatever interval you feel works well.

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Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain