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