1.\" $NetBSD: pipe.2,v 1.6 1995/02/27 12:35:27 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 February 17, 2011 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.Fo pipe 46.Fa "int fildes[2]" 47.Fc 48.Sh DESCRIPTION 49The 50.Fn pipe 51function 52creates a 53.Em pipe 54(an object that allows unidirectional data flow) 55and allocates a pair of file descriptors. 56The first descriptor connects to the 57.Em read end 58of the pipe; 59the second connects to the 60.Em write end . 61.Pp 62Data 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 70to be the write end of the pipe; 71the sink's standard input is set up 72to be the read end of the pipe. 73The pipe itself persists 74until all of its associated descriptors are closed. 75.Pp 76A pipe whose read or write end has been 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 generation of the 87.Dv SIGPIPE 88signal can be suppressed using the 89.Dv F_SETNOSIGPIPE 90fcntl command. 91.Sh RETURN VALUES 92On successful creation of the pipe, zero is returned. Otherwise, 93a value of -1 is returned and the variable 94.Va errno 95set to indicate the 96error. 97.Sh ERRORS 98The 99.Fn pipe 100call will fail if: 101.Bl -tag -width Er 102.\" =========== 103.It Bq Er EFAULT 104The 105.Fa fildes 106buffer is in an invalid area of the process's address 107space. 108.\" =========== 109.It Bq Er EMFILE 110Too many descriptors are active. 111.\" =========== 112.It Bq Er ENFILE 113The system file table is full. 114.El 115.Sh SEE ALSO 116.Xr sh 1 , 117.Xr fork 2 , 118.Xr read 2 , 119.Xr socketpair 2 , 120.Xr fcntl 2 , 121.Xr write 2 122.Sh HISTORY 123A 124.Fn pipe 125function call appeared in 126.At v6 . 127