Historically I recall observing the same thing, that you could even `cat` a directory and get garbage printed to your terminal. However I think it was widely regarded as a misfeature and there's generally been a move towards the `read` syscall itself returning EISDIR as noted elsewhere in the thread. I've just tested linux (3.10.0-693.5.2.el7) and OpenBSD (6.4) and they both display this behaviour. OSX (Darwin kernel 19.5.0) reports "Operation not supported" trying to cat a directory but I'm not sure how to check the syscalls here.