Re: AC_CHECK_FILES on /dev/stdin

[Keith MARSHALL]

Hi David,

David Fang wrote:
> I naively tried to use AC_CHECK_FILE(S) on /dev/stdin /dev/stdout
> and /dev/stderr to detect their presence, but the test result is
> 'no' for these 'files'.

These are not real devices.  You may find entries in /dev, which
suggest otherwise, but look closely:  if they exist at all, they
will be symbolic links to fd entities in the /proc pseudo-file
system; i.e. they aren't connected to real files or devices, but
exist as virtual properties of processes.

> The result is 'yes', however, for /dev/null.

This, OTOH, is a real device, in the sense that the kernel manages
it with a device driver which simply returns EOF on read, or discards
all data written.

> Is there a more appropriate test for the presence of these special
> files?  or do I need to roll my own macro-test using something like
> "test -f"?  (Or am I checking for something that should/need not be
> checked?)  Suggestions?

You don't need to check for them.  Unless you explicitly force it to
be otherwise, *every* process is *guaranteed* to have stdin, stdout
and stderr streams;  you must be doing something very esoteric, if
you find a need to refer to /dev/stdin, /dev/stdout or /dev/stderr.

HTH,
Keith.