Retaining input file name in the output file

I’m not yet fluent with TCL, so the explanations I’ve found while searching are vague to me.

I want to set up fileset-local and process files dropped in the directory. In the outbound directory, I want an output file whose name is or contains the input file name from which the data originated, such as export.$ORIGINALFILENAME.  

Can someone give me detail on how/where the metadata for this is stored, and the retrieved, and in it’s simplest form? (as in hopefully a 1 line storage command, etc)

5.8

Thanks,

Scott