You already have all the pieces that you need:
- In your root node you show how you get the command line arguments.
- bart showed you how to
- get the pathname of the project.txt file using File::Basename,
- parse the value out of the REVISION_LOCATION: line, and
- turn that filename from relative to absolute using File::Spec's rel2abs, using the pathname of project.txt as the base.
If you're unsure on how to open the project.txt file instead of using the magic while(<>) that bart used, please see "Files and I/O" in perlintro.
Updated wording slightly.