People seem to be missing character classes like [[:upper:]]. If you need some other sort of range in a portable script, say, just make sure you set LC_COLLAT

People seem to be missing character classes like [[:upper:]]. If you need some other sort of range in a portable script, say, just make sure you set LC_COLLATE. And if you're testing with GNU sort, use --debug to check what it's actually doing in case you don't have the definition for the current LC_COLLATE, for instance.