1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)pipe.2 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD: src/lib/libc/sys/pipe.2,v 1.13.2.5 2001/12/14 18:34:01 ru Exp $ 34.\" $DragonFly: src/lib/libc/sys/pipe.2,v 1.2 2003/06/17 04:26:47 dillon Exp $ 35.\" 36.Dd June 4, 1993 37.Dt PIPE 2 38.Os 39.Sh NAME 40.Nm pipe 41.Nd create descriptor pair for interprocess communication 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In unistd.h 46.Ft int 47.Fn pipe "int *fildes" 48.Sh DESCRIPTION 49The 50.Fn pipe 51function 52creates a 53.Em pipe , 54which is an object allowing 55bidirectional data flow, 56and allocates a pair of file descriptors. 57.Pp 58By convention, the first descriptor is normally used as the 59.Em read end 60of the pipe, 61and the second is normally the 62.Em write end , 63so that data written to 64.Fa fildes[1] 65appears on (i.e., can be read from) 66.Fa fildes[0] . 67This allows the output of one program to be 68sent 69to another program: 70the source's standard output is set up to be 71the write end of the pipe, 72and the sink's standard input is set up to be 73the read end of the pipe. 74The pipe itself persists until all its associated descriptors are 75closed. 76.Pp 77A pipe that has had an end closed is considered 78.Em widowed . 79Writing on such a pipe causes the writing process to receive 80a 81.Dv SIGPIPE 82signal. 83Widowing a pipe is the only way to deliver end-of-file to a reader: 84after the reader consumes any buffered data, reading a widowed pipe 85returns a zero count. 86.Pp 87The bidirectional nature of this implementation of pipes is not 88portable to older systems, so it is recommended to use the convention 89for using the endpoints in the traditional manner when using a 90pipe in one direction. 91.Sh RETURN VALUES 92.Rv -std pipe 93.Sh ERRORS 94The 95.Fn pipe 96call will fail if: 97.Bl -tag -width Er 98.It Bq Er EMFILE 99Too many descriptors are active. 100.It Bq Er ENFILE 101The system file table is full. 102.It Bq Er EFAULT 103The 104.Fa fildes 105buffer is in an invalid area of the process's address 106space. 107.El 108.Sh SEE ALSO 109.Xr sh 1 , 110.Xr fork 2 , 111.Xr read 2 , 112.Xr socketpair 2 , 113.Xr write 2 114.Sh HISTORY 115A 116.Fn pipe 117function call appeared in 118.At v3 . 119.Pp 120Bidirectional pipes were first used on 121.At V.4 . 122