1.\" $NetBSD: pipe.2,v 1.9 1997/09/17 23:50:08 cgd Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)pipe.2 8.1 (Berkeley) 6/4/93 35.\" 36.Dd June 4, 1993 37.Dt PIPE 2 38.Os BSD 4 39.Sh NAME 40.Nm pipe 41.Nd create descriptor pair for interprocess communication 42.Sh SYNOPSIS 43.Fd #include <unistd.h> 44.Ft int 45.Fn pipe "int fildes[2]" 46.Sh DESCRIPTION 47The 48.Fn pipe 49function 50creates a 51.Em pipe , 52which is an object allowing 53unidirectional data flow, 54and allocates a pair of file descriptors. 55The first descriptor connects to the 56.Em read end 57of the pipe, 58and the second connects to the 59.Em write end , 60so that data written to 61.Fa fildes[1] 62appears on (i.e., can be read from) 63.Fa fildes[0] . 64This allows the output of one program to be 65sent 66to another program: 67the source's standard output is set up to be 68the write end of the pipe, 69and the sink's standard input is set up to be 70the read end of the pipe. 71The pipe itself persists until all its associated descriptors are 72closed. 73.Pp 74A pipe whose read or write end has been closed is considered 75.Em widowed . 76Writing on such a pipe causes the writing process to receive 77a 78.Dv SIGPIPE 79signal. 80Widowing a pipe is the only way to deliver end-of-file to a reader: 81after the reader consumes any buffered data, reading a widowed pipe 82returns a zero count. 83.Sh RETURN VALUES 84On successful creation of the pipe, zero is returned. Otherwise, 85a value of -1 is returned and the variable 86.Va errno 87set to indicate the 88error. 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 read 2 , 107.Xr write 2 , 108.Xr fork 2 , 109.Xr socketpair 2 110.Sh STANDARDS 111The 112.Fn pipe 113function conforms to 114.St -p1003.1-90 . 115.Sh HISTORY 116A 117.Fn pipe 118function call appeared in 119.At v6 . 120