1.\" $NetBSD: pipe.2,v 1.18 2002/10/01 18:10:45 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. 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 July 17, 1994 37.Dt PIPE 2 38.Os 39.Sh NAME 40.Nm pipe 41.Nd create descriptor pair for interprocess communication 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.Fd #include \*[Lt]unistd.h\*[Gt] 46.Ft int 47.Fn pipe "int fildes[2]" 48.Sh DESCRIPTION 49The 50.Fn pipe 51function 52creates a 53.Em pipe , 54which is an object allowing 55unidirectional data flow, 56and allocates a pair of file descriptors. 57The first descriptor connects to the 58.Em read end 59of the pipe, 60and the second connects to 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 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.Sh RETURN VALUES 86On successful creation of the pipe, zero is returned. 87Otherwise, a value of -1 is returned and the variable 88.Va errno 89set to indicate the 90error. 91.Sh ERRORS 92The 93.Fn pipe 94call will fail if: 95.Bl -tag -width Er 96.It Bq Er EMFILE 97Too many descriptors are active. 98.It Bq Er ENFILE 99The system file table is full. 100.It Bq Er EFAULT 101The 102.Fa fildes 103buffer is in an invalid area of the process's address space. 104The reliable detection of this error cannot be guaranteed; when not 105detected, a signal may be delivered to the process, indicating an 106address violation. 107.El 108.Sh SEE ALSO 109.Xr sh 1 , 110.Xr fork 2 , 111.Xr read 2 , 112.Xr socketpair 2 , 113.Xr write 2 114.Sh STANDARDS 115The 116.Fn pipe 117function conforms to 118.St -p1003.1-90 . 119.Sh HISTORY 120A 121.Fn pipe 122function call appeared in 123.At v6 . 124