Dynamic FileName and Directory - UDF

My scenario is to get Target Directory Name based on part of Filename. How can I do that using UDF. I will select adapter specific parametrs and like to change using UDF. TO achive this I will create a dummy field names in the target structure. Can someone let give me UDF code?.

For Example: Source FileName : SD00123456Prod.csv

Target Directory Should be /Sales/

Target File: Prod.csv

Thanks for any help.