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From: dkeisen@leland.Stanford.EDU (Dave Eisen)
Newsgroups: comp.unix.questions,comp.unix.programmer
Subject: Re: How do I tell if STDIN is a PIPE?
Message-ID: <1991Jun3.141144.23620@leland.Stanford.EDU>
Date: 3 Jun 91 14:11:44 GMT
References: <1991May26.172328.713@arizona.edu> <1991May30.101153.27842@thunder.mcrcim.mcgill.edu> <653@eskimo.celestial.com>
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In article <653@eskimo.celestial.com> nanook@eskimo.celestial.com (Robert Dinse) writes: 
> How do I tell whether stdin is coming from a pipe?

>> In article <1991May26.172328.713@arizona.edu>, jjr@ace.ece.arizona.edu (Jeffrey J. Rodriguez) writes:
>
>     Try:
>	fstat(0, &s);
>	if(s.st_mode & S_IFIFO)
>		printf("Stdin is a pipe.\n");
>	else
>		printf("Stdin is not a pipe.\n");

This doesn't work everywhere, in particular, it doesn't work on the machine I
am posting from. s.st_mode & S_IFREG (which, by the way, is what you should
be testing for) is 0 when stdin is a pipe. This doesn't seem to be consistently
done across Unices.

That is one of the reasons I suggested that the original poster just try his
seek and see what happens --- as far as I know, any UNIX asked to 
seek on a file type that is unseekable will fail with errno set to ESPIPE.



-- 
Dave Eisen                           dkeisen@leland.Stanford.EDU
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