Hey Richard, there are a unknowns to your question like, how are you going to derive the new file name? Is it based on the current file name? Is it just a crop of the current file name? Is it some totally new file name? Is the new file name based on current date/time? etc, etc, etc.
With that said, here is an example that just takes the first 8 characters of the existing file name to use for the rename.