Having this depend on env vars is an anti-feature in my mind. It's much harder to ensure env vars are set to the "right" values in all situations then it is to just use some well-known paths.
Come on, you just use a fallback if it's unset, you can even use your "well-known" paths for that if you want to. Don't pretend this harder than it actually is! This is like lesson 1 to using environmental variables, it's like saying you never free your mallocs because it's "much harder" that way! The OP site even provides code examples for popular languages, how can you imply that randomly littering your user's $HOME directory is the viable alternative here?
