You're right Matt, (source) [or maybe (source dir)] is the nupic checkout directory itself (ex: /Volumes/DavidRagazzi/Desktop/nupic-master), not a literal value. I'm avoiding use env variables because this avoid a newbie have to read CMakeLists or shell scripts to find definitions. Your idea is good, we could add a line saying that (source dir) is the current location where user downloaded the repository.