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From: mouse@mcgill-vision.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: dup2 issue
Message-ID: <759@mcgill-vision.UUCP>
Date: Wed, 6-May-87 02:56:45 EDT
Article-I.D.: mcgill-v.759
Posted: Wed May  6 02:56:45 1987
Date-Received: Thu, 14-May-87 01:32:33 EDT
References: <1004@copper.TEK.COM>
Distribution: world
Organization: McGill University, Montreal
Lines: 43
Keywords: dup2

In article <1004@copper.TEK.COM>, stevesu@copper.TEK.COM (Steve Summit) writes:
> [what does dup2 do with two identical arguments?  Question arises
> from something like]

> 	close(sv[1]);
> 	close(0);
> 	close(1);
> 	close(2);
> 	dup(sv[0]);
> 	dup(sv[0]);
> 	dup(sv[0]);
> 	close(sv[0]);

> This code fails if it is invoked with 0, 1, or 2 already closed,

> I changed the code to

> 	if(sv[0] != 0)
> 		dup2(sv[0], 0);
> 	if(sv[0] != 1)
> 		dup2(sv[0], 1);
> 	if(sv[0] != 2)
> 		dup2(sv[0], 2);
> 	if(sv[0] > 2)
> 		close(sv[0]);

> but I wondered if the first three if's were strictly necessary.

Well, I would suggest you write it as

	if (sv[0] != fileno(stdin))
	 { dup2(sv[0],fileno(stdin));
	   close(sv[0]);
	 }
	dup2(fileno(stdin),fileno(stdout));
	dup2(fileno(stdin),fileno(stderr));

[this line to patch around stupid counterproductive 50% rule]
[this line to patch around stupid counterproductive 50% rule]

					der Mouse

				(mouse@mcgill-vision.uucp)