Calling a shell script

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I have created a stack which uses a Form to enable a user to download a file. The option to download a file is only available to a user after they login to my site.

After the file in downloaded, I need to run a shell script to parse the file that was just downloaded. I need to know the user that downloaded the file and the path to the file. How do I call the shell script and provide the parameters when the file is downloaded?