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From: worley@compass.com (Dale Worley)
Newsgroups: comp.lang.perl
Subject: problem redirecting STDOUT to pipe
Message-ID: <1990Jul16.161925.9869@uvaarpa.Virginia.EDU>
Date: 16 Jul 90 16:19:25 GMT
Sender: mmdf@uvaarpa.Virginia.EDU (Uvaarpa Mail System)
Reply-To: worley@compass.com
Organization: The Internet
Lines: 27


   X-Name: Randal Schwartz

   The short answer, which may lead you to more insight, is that you also
   need to think of the stdout of the "dd" command.  [...]

The problem is that this loses...  You have to always put STDOUT on fd
1, because otherwise if you exec something its output will go into
never-never land.

The proper way to handle pipes and redirection is to first create a
pipe pair (which goes on fd's 7 and 8, say), then fork, then each
process closes stdin/stdout/whatever and dup's the input or output
side of the pipe into the correct fd's, and then both close fd's 7 and
8 (to clean up).  With this method, each process can put either end of
the pipe on whatever fd's it wants.

While we're at it, what's the method for creating a pipe pair in Perl?
I can't find anything in the manual that does not also cause forking.
I'm sure this has been discussed before, but I don't remember the
answer and now I'm in the throes of a "redirect both STDIN and STDOUT
to a subprocess" program...

Dale Worley		Compass, Inc.			worley@compass.com
--
"If you could have any amount of money... How much would you want?"
"All of it."