If you're looking to parse a path into directories and the filename, use File::Basename or File::Spec. If you're just creating a path for the output (log) file, though, I'm not sure why you need the short format in the first place. You should be able to use long (complete) directory and file names on windows - it works for me.

Update: I just realized your question might be refering to parsing the command line, not just the filenames. If that's the case you'll have to look at @ARGV (see perlvar), which contains command line arguments. You might also want to consider using something like Getopt rather than pulling things out of @ARGV yourself.