Of course, this still ignores case-insensitive volumes, as well as paths containing «.» and «..». But what can you do? (Well, «.» can be addressed, but there's no obvious solution if any exist for the rest.)

There's also portability issues like what File::Spec handles. Volumes and different path separators, etc. You can also be processing a list of paths generated on a different system (e.g. processing windows paths on unix).