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From: bharat@cf-cm.computing-maths.cardiff.ac.uk (Bharat Mediratta)
Newsgroups: comp.unix.wizards
Subject: Re: Taking Control of stdin/stdout of a slave process
Message-ID: <1991Mar14.140749.24337@cm.cf.ac.uk>
Date: 14 Mar 91 14:07:49 GMT
References: <1991Mar13.163756.26785@evax.arl.utexas.edu>
Sender: news@cm.cf.ac.uk (USENET News System)
Organization: University of Wales College of Cardiff
Lines: 49

In article <1991Mar13.163756.26785@evax.arl.utexas.edu> rduff@evax.arl.utexas.edu (Robert Duff) writes:
>
>I am interested in starting a UNIX process from a program and having the
>slave process' stdin and stdout piped through FILE*'s in the master process.
>
>I have worked with popen(), but that only allows one-way piping.
>How can I get both directions piped to my controller process?

Try using pipe(3), and dup2(3):

#define READ 0
#define WRITE 1

main()
{
	int master[2], slave[2];
	int slave_out, slave_in;

	if ((pipe(local) < 0) || (pipe(remote) < 0)) {
	    fprintf(stderr, "Pipes failed!\n");
	    exit(1);
	}

	if (fork() == 0) {
		dup2(master[READ], 0);
		dup2(slave[WRITE], 1);
		dup2(slave[WRITE], 2);

		/* execl the job */
	} else {
		char ch;
		to_slave = slave[WRITE];
		from_slave = slave[READ];	
		while (read(from_slave,&ch,1)==1)
			printf("%c", ch);
	}
}	

This ought to do the trick.  Writing to 'to_slave' will
send bytes to the slave process, and reading from 'from_slave'
will read the output from the slave process.  

Cheers!
-Bharat
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