1.\" Copyright (c) 1980, 1991 Regents of the University of California. 2.\" 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.\" from: @(#)pipe.2 6.3 (Berkeley) 3/10/91 33.\" $Id: pipe.2,v 1.4 1993/11/29 21:25:26 jtc Exp $ 34.\" 35.Dd March 10, 1991 36.Dt PIPE 2 37.Os BSD 4 38.Sh NAME 39.Nm pipe 40.Nd create descriptor pair for interprocess communication 41.Sh SYNOPSIS 42.Fd #include <unistd.h> 43.Ft int 44.Fn pipe "int *fildes" 45.Sh DESCRIPTION 46The 47.Fn pipe 48function 49creates a 50.Em pipe , 51which is an object allowing 52unidirectional data flow, 53and allocates a pair of file descriptors. 54The first descriptor connects to the 55.Em read end 56of the pipe, 57and the second connects to 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 whose read or write end has been 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 83Pipes are really a special case of the 84.Xr socketpair 2 85call and, in fact, are implemented as such in the system. 86.Sh RETURN VALUES 87On successful creation of the pipe, zero is returned. Otherwise, 88a value of -1 is returned and the variable 89.Va errno 90set to indicate the 91error. 92.Sh ERRORS 93The 94.Fn pipe 95call will fail if: 96.Bl -tag -width Er 97.It Bq Er EMFILE 98Too many descriptors are active. 99.It Bq Er ENFILE 100The system file table is full. 101.It Bq Er EFAULT 102The 103.Fa fildes 104buffer is in an invalid area of the process's address 105space. 106.El 107.Sh SEE ALSO 108.Xr sh 1 , 109.Xr read 2 , 110.Xr write 2 , 111.Xr fork 2 , 112.Xr socketpair 2 113.Sh HISTORY 114A 115.Fn pipe 116function call appeared in 117.At v6 . 118