POSIX IO – How Portable are /dev/stdin, /dev/stdout, and /dev/stderr

file-descriptorsioportabilityposix

Occasionally I need to specify a "path-equivalent" of one of the standard IO streams (stdin, stdout, stderr). Since 99% of the time I work with Linux, I just prepend /dev/ to get /dev/stdin, etc., and this "seems to do the right thing". But, for one thing, I've always been uneasy about such a rationale (because, of course, "it seems to work" until it doesn't). Furthermore, I have no good sense for how portable this maneuver is.

So I have a few questions:

  1. In the context of Linux, is it safe (yes/no) to equate stdin,
    stdout, and stderr with /dev/stdin, /dev/stdout, and
    /dev/stderr?

  2. More generally, is this equivalence "adequately portable"?

I could not find any POSIX references.

Best Answer

It's been available on Linux back into its prehistory. It is not POSIX, although many actual shells (including AT&T ksh and bash) will simulate it if it's not present in the OS; note that this simulation only works at the shell level (i.e. redirection or command line parameter, not as explicit argument to e.g. open()). That said, it should be available on most commercial Unix systems, one way or another (sometimes it's spelled /dev/fd/N for various integers N, but most systems with that will provide symlinks as Linux and *BSD do).

Related Question