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.\" 35.Dd June 4, 1993 36.Dt PIPE 2 37.Os 38.Sh NAME 39.Nm pipe 40.Nd create descriptor pair for interprocess communication 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In unistd.h 45.Ft int 46.Fn pipe "int *fildes" 47.Sh DESCRIPTION 48The 49.Fn pipe 50function 51creates a 52.Em pipe , 53which is an object allowing 54bidirectional data flow, 55and allocates a pair of file descriptors. 56.Pp 57By convention, the first descriptor is normally used as the 58.Em read end 59of the pipe, 60and the second is normally the 61.Em write end , 62so that data written to 63.Fa fildes[1] 64appears on (i.e., can be read from) 65.Fa fildes[0] . 66This allows the output of one program to be 67sent 68to another program: 69the source's standard output is set up to be 70the write end of the pipe, 71and the sink's standard input is set up to be 72the read end of the pipe. 73The pipe itself persists until all its associated descriptors are 74closed. 75.Pp 76A pipe that has had an end closed is considered 77.Em widowed . 78Writing on such a pipe causes the writing process to receive 79a 80.Dv SIGPIPE 81signal. 82Widowing a pipe is the only way to deliver end-of-file to a reader: 83after the reader consumes any buffered data, reading a widowed pipe 84returns a zero count. 85.Pp 86The bidirectional nature of this implementation of pipes is not 87portable to older systems, so it is recommended to use the convention 88for using the endpoints in the traditional manner when using a 89pipe in one direction. 90.Sh RETURN VALUES 91.Rv -std pipe 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 fork 2 , 110.Xr read 2 , 111.Xr socketpair 2 , 112.Xr write 2 113.Sh HISTORY 114A 115.Fn pipe 116function call appeared in 117.At v3 . 118.Pp 119Bidirectional pipes were first used on 120.At V.4 . 121