*EDIT* Edited subject as well as post to reflect more accurately what I am looking to do.
Title. I'd like to build a single script for all my backups but I need 2 separate functions for it. Backing my data partition to the usb hdds is 1, other is to keep a current backup of my /var/cache/apt/archives. As of right now I have them as 2 separate scripts. How can I call a specific function from the command line ( for cron entries )?