Copy autonumber field to a single line field using deluge.

Copy autonumber field to a single line field using deluge.

hello everyone. 

Silly question it might be as a basic script. but not had to do it before. I can't get the unique values up in normal update fields. 

How would I go about in the customers/accounts module - There is an autonumber field that I want to paste automatically into a unique value, single line field. It will be a function I can then hopefully attach to a workflow rule to trigger on record creation. 

Also one I would like to run in bulk once!

Thanks in advance. 
Nick