Programmatically obtaining file uploaded to a custom field

Hello all,
I’ve set up an RT queue with a custom field with the type “upload one file”. I need to obtain the file from the custom field to process in a perl script. I’ve been able to the REST API to get a file that was attached to a ticket, but I can’t seem to find a way to get a file that was uploaded into a custom field.

Is the functionality I’m looking for available with REST? Is there another API that I could use?

Has anyone done something similar?

–Jeff Ilgen