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From: maart@cs.vu.nl (Maarten Litmaath)
Newsgroups: comp.unix.questions
Subject: Re: Reopening stdin
Message-ID: <8688@star.cs.vu.nl>
Date: 8 Jan 91 19:17:01 GMT
References: <5200@trantor.harris-atd.com> <8685@star.cs.vu.nl> <5208@trantor.harris-atd.com>
Sender: news@cs.vu.nl
Reply-To: maart@cs.vu.nl (Maarten Litmaath)
Organization: VU Dept. of Computer Science, Amsterdam, The Netherlands
Lines: 28

In article <5208@trantor.harris-atd.com>,
	chuck@trantor.harris-atd.com (Chuck Musciano) writes:
)...
)> 	main()
)> 	{
)> 		int	fd, i;
)> 
)> 		close(0);
)> 		fd = open("/etc/passwd", 0);
)> 		dup2(fd, 0);
)> 		i = system("cat");
)> 		exit(i & 0377 ? i | 0200 : i >> 8);
)> 	}
)...
)     I checked dup2(), and it is returning 0, as you would expect.  In the
)case of dup2(0, 0), I tried closing stdin, calling open(), and verified
)that I got 0 as the descriptor.  I then skipped the dup2 call, called
)system(), and it still failed!

What about this: note that in the example I forgot a close(fd) statement
after the dup2() call; now I expect that you did _not_ forget it in _your_
program, in which case you are closing stdin yourself again!

If this still doesn't explain it, could you post or email a minimal
piece of code that shows the problem?
--
nlp@berlin.mt.cs.cmu.edu: "I heard that an Awk was spotted in Sherwood forest."
rmk@frog.UUCP (Rick Kelly): "It was seen running in the background."