1.\" $NetBSD: pipe.2,v 1.22 2004/05/13 10:20:58 wiz 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. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)pipe.2 8.1 (Berkeley) 6/4/93 31.\" 32.Dd July 17, 1994 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[2]" 44.Sh DESCRIPTION 45The 46.Fn pipe 47function 48creates a 49.Em pipe , 50which is an object allowing 51unidirectional data flow, 52and allocates a pair of file descriptors. 53The first descriptor connects to the 54.Em read end 55of the pipe, 56and the second connects to the 57.Em write end , 58so that data written to 59.Fa fildes[1] 60appears on (i.e., can be read from) 61.Fa fildes[0] . 62This allows the output of one program to be 63sent 64to another program: 65the source's standard output is set up to be 66the write end of the pipe, 67and the sink's standard input is set up to be 68the read end of the pipe. 69The pipe itself persists until all its associated descriptors are 70closed. 71.Pp 72A pipe whose read or write end has been closed is considered 73.Em widowed . 74Writing on such a pipe causes the writing process to receive 75a 76.Dv SIGPIPE 77signal. 78Widowing a pipe is the only way to deliver end-of-file to a reader: 79after the reader consumes any buffered data, reading a widowed pipe 80returns a zero count. 81.Sh RETURN VALUES 82On successful creation of the pipe, zero is returned. 83Otherwise, a value of \-1 is returned and the variable 84.Va errno 85set to indicate the 86error. 87.Sh ERRORS 88The 89.Fn pipe 90call will fail if: 91.Bl -tag -width Er 92.It Bq Er EMFILE 93Too many descriptors are active. 94.It Bq Er ENFILE 95The system file table is full. 96.It Bq Er EFAULT 97The 98.Fa fildes 99buffer is in an invalid area of the process's address space. 100The reliable detection of this error cannot be guaranteed; when not 101detected, a signal may be delivered to the process, indicating an 102address violation. 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 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