// Copyright (c) 1986, 1993
//	The Regents of the University of California.  All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
// 3. All advertising materials mentioning features or use of this software
//    must display the following acknowledgement:
//	This product includes software developed by the University of
//	California, Berkeley and its contributors.
// 4. Neither the name of the University nor the names of its contributors
//    may be used to endorse or promote products derived from this software
//    without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
//
//	@(#)pipe.c	8.1 (Berkeley) 6/8/93
//
#include <stdio.h>

#define DATA "Bright star, would I were steadfast as thou art . . ."

/*
 * This program creates a pipe, then forks.  The child communicates to the
 * parent over the pipe. Notice that a pipe is a one-way communications
 * device.  I can write to the output socket (sockets[1], the second socket
 * of the array returned by pipe()) and read from the input socket
 * (sockets[0]), but not vice versa.
 */

main()
{
	int sockets[2], child;

	/* Create a pipe */
	if (pipe(sockets) < 0) {
		perror("opening stream socket pair");
		exit(10);
	}

	if ((child = fork()) == -1)
		perror("fork");
	else if (child) {
		char buf[1024];

		/* This is still the parent.  It reads the child's message. */
		close(sockets[1]);
		if (read(sockets[0], buf, 1024) < 0)
			perror("reading message");
		printf("-->%s\en", buf);
		close(sockets[0]);
	} else {
		/* This is the child.  It writes a message to its parent. */
		close(sockets[0]);
		if (write(sockets[1], DATA, sizeof(DATA)) < 0)
			perror("writing message");
		close(sockets[1]);
	}
}
.