1*075022b3Sagc .\" $NetBSD: pipe.c,v 1.3 2003/08/07 10:30:50 agc Exp $ 26d400d56Sperry .\" 3d9158b13Scgd .\" Copyright (c) 1986, 1993 4d9158b13Scgd .\" The Regents of the University of California. All rights reserved. 5d9158b13Scgd .\" 6d9158b13Scgd .\" Redistribution and use in source and binary forms, with or without 7d9158b13Scgd .\" modification, are permitted provided that the following conditions 8d9158b13Scgd .\" are met: 9d9158b13Scgd .\" 1. Redistributions of source code must retain the above copyright 10d9158b13Scgd .\" notice, this list of conditions and the following disclaimer. 11d9158b13Scgd .\" 2. Redistributions in binary form must reproduce the above copyright 12d9158b13Scgd .\" notice, this list of conditions and the following disclaimer in the 13d9158b13Scgd .\" documentation and/or other materials provided with the distribution. 14*075022b3Sagc .\" 3. Neither the name of the University nor the names of its contributors 15d9158b13Scgd .\" may be used to endorse or promote products derived from this software 16d9158b13Scgd .\" without specific prior written permission. 17d9158b13Scgd .\" 18d9158b13Scgd .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19d9158b13Scgd .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20d9158b13Scgd .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21d9158b13Scgd .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22d9158b13Scgd .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23d9158b13Scgd .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24d9158b13Scgd .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25d9158b13Scgd .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26d9158b13Scgd .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27d9158b13Scgd .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28d9158b13Scgd .\" SUCH DAMAGE. 29d9158b13Scgd .\" 30d9158b13Scgd .\" @(#)pipe.c 8.1 (Berkeley) 6/8/93 31d9158b13Scgd .\" 32d9158b13Scgd #include <stdio.h> 33d9158b13Scgd 34d9158b13Scgd #define DATA "Bright star, would I were steadfast as thou art . . ." 35d9158b13Scgd 36d9158b13Scgd /* 37d9158b13Scgd * This program creates a pipe, then forks. The child communicates to the 38d9158b13Scgd * parent over the pipe. Notice that a pipe is a one-way communications 39d9158b13Scgd * device. I can write to the output socket (sockets[1], the second socket 40d9158b13Scgd * of the array returned by pipe()) and read from the input socket 41d9158b13Scgd * (sockets[0]), but not vice versa. 42d9158b13Scgd */ 43d9158b13Scgd 44d9158b13Scgd main() 45d9158b13Scgd { 46d9158b13Scgd int sockets[2], child; 47d9158b13Scgd 48d9158b13Scgd /* Create a pipe */ 49d9158b13Scgd if (pipe(sockets) < 0) { 50d9158b13Scgd perror("opening stream socket pair"); 51d9158b13Scgd exit(10); 52d9158b13Scgd } 53d9158b13Scgd 54d9158b13Scgd if ((child = fork()) == -1) 55d9158b13Scgd perror("fork"); 56d9158b13Scgd else if (child) { 57d9158b13Scgd char buf[1024]; 58d9158b13Scgd 59d9158b13Scgd /* This is still the parent. It reads the child's message. */ 60d9158b13Scgd close(sockets[1]); 61d9158b13Scgd if (read(sockets[0], buf, 1024) < 0) 62d9158b13Scgd perror("reading message"); 63d9158b13Scgd printf("-->%s\en", buf); 64d9158b13Scgd close(sockets[0]); 65d9158b13Scgd } else { 66d9158b13Scgd /* This is the child. It writes a message to its parent. */ 67d9158b13Scgd close(sockets[0]); 68d9158b13Scgd if (write(sockets[1], DATA, sizeof(DATA)) < 0) 69d9158b13Scgd perror("writing message"); 70d9158b13Scgd close(sockets[1]); 71d9158b13Scgd } 72d9158b13Scgd } 73