Config::Any (what I personally use) will read a file with only keys=values (it will consider it as an INI file, without "directories") and in bash, you just source such a file.

IIRC you can't read a .xml file under bash, either, so XML is kind of off-limits for said requirement. I respect your opinion, but I still think that inventing the wheel for reading config files is a waste of time.

As for your mentioned post, my configs do all four items you put there, just loading with Config::Any and traversing in the appropriate order.