Lon,
It would be cool if PM had a variable that allowed selecting the left or right x characters of the {filenamebase} or better yet any variable.
That is definitely coming in version 4.5. I added that feature a few weeks ago.
Variables, substring extraction works like this:
{variable:start:count}
Where <start> is the zero-based index of the character you want to start extracting from, or use negative numbers to extract from the end. <count> is the number of characters to extract.
So you can do things like this:
{filenamebase:0,5} // extract five characters from filenamebase starting at character 0
{filenamebase:-5,5} // extract five characters from the end of filenamebase
{filenamebase:5,2} // extract two characters from character 5 of filenamebase
This makes it easy to grab substrings from variables and build new strings from them.
-Kirk