Thanks Alexander. I wanted to upload a file and process it, and then dynamically create a web page that would allow a user to upload the same file again and process it in some other way. I could just store the file on the server the first time it was uploaded and use it again in the second processing phase, but I don't want to keep a permanent copy of the file on the server, and I don't see any way of ensuring the file gets deleted (the user might decide not to initiate the second processing phase). I thought of using <body onUnLoad="some_script"> but I don't think this works if the user just shuts down the browser instead of navigating away from the page. I also tried using Javascript which gets called when the form's submit button is clicked, but this doesn't work either. I guess I could use a cron job to get rid of the file on the server.
Let me know if I have overlooked something.
J.