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    This had the useful result that you could no longer accidentally cat a directory and get all sorts of gibberish spewed on your screen, without requiring cat (and everything else that reads files) to explicitly refuse to touch directories. This feature does not seem to have spread to Solaris or the *BSDs, at least as far as I can see.

    Failing a read(2) with EISDIR was introduced in OpenBSD 6.1 (released in 2017). See this comment and the rest of the thread for some additional insights into history.