Re: Re-casing directories on case-insensitive systems

Linus Torvalds <torvalds@linux-foundation.org> writes:

Ah, those young whippersnappers who think they are so smart... there is a history to that, you know. Early character sets (like those on punch cards) had just capital letters. Even when lowercase letters were introduced, those tended to use more space (12 instead of 6 bit) and be harder to print (and the line printers who churned out 40 lines per second did not bother with such finesse, anyway). But capital letters are not designed for readability of long lines. So when printing or even screen terminals came into use, one tended to prefer writing in lowercase letters. Which actually had the uppercase code points usually. Some early microcomputers (for which CP/M was designed) actually were hooked up with a "standard" 50 or 110 Baud teletype as I/O device, and those tended to have only lowercase letters, too, in their basic incantations. So CP/M, not knowing which kind of input device would be used and whether it would prefer (or offer exclusively) upper or lower case, had case-insensitive commands, and consequently also case-insensitive file names. And QDOS (whence MSDOS) was basically intended to be a CP/M ripoff.

OS X has an Apple inheritance, Apple has the same inheritance as other microcomputers which includes a case-insensitive BASIC interpreter (BASIC again coming from old teletype times). It is, again, a decision to drag along old history.

But actually, there is more to it nowadays: two file names containing ü, but one with a single letter and one with combining accent, look exactly the same. If they don't act exactly the same, one opens up quite a hole for spoofing attacks. Well, probably hard to avoid (since things like uppercase Alpha and uppercase A look the same and need to be different code points, too). But one also opens a can of worms for confusion. So the problem of canonical file names does not go away just with case sensitivity.

It is not like Linux does not support some case-insensitive file system types, too. So the same problems can be had there as well.