1.\" $NetBSD: pipe.2,v 1.30 2014/02/22 17:26:41 dholland 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 January 23, 2012 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.In unistd.h 45.In fcntl.h 46.Ft int 47.Fn pipe2 "int fildes[2]" "int flags" 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.Pp 86The 87.Fn pipe2 88function 89behaves exactly like 90.Fn pipe 91only it allows extra 92.Fa flags 93to be set on the returned file descriptor. 94The following flags are valid: 95.Bl -tag -width O_NONBLOCK -offset indent 96.It Dv O_CLOEXEC 97Set the 98.Dq close-on-exec 99property. 100.It Dv O_NONBLOCK 101Sets non-blocking I/O. 102.It Dv O_NOSIGPIPE 103Return 104.Er EPIPE 105instead of raising 106.Dv SIGPIPE . 107.El 108.Sh RETURN VALUES 109On successful creation of the pipe, zero is returned. 110Otherwise, a value of \-1 is returned and the variable 111.Va errno 112set to indicate the 113error. 114.Sh ERRORS 115The 116.Fn pipe 117and 118.Fn pipe2 119calls will fail if: 120.Bl -tag -width Er 121.It Bq Er EFAULT 122The 123.Fa fildes 124buffer is in an invalid area of the process's address space. 125The reliable detection of this error cannot be guaranteed; when not 126detected, a signal may be delivered to the process, indicating an 127address violation. 128.It Bq Er EMFILE 129Too many descriptors are active. 130.It Bq Er ENFILE 131The system file table is full. 132.El 133.Pp 134.Fn pipe2 135will also fail if: 136.Bl -tag -width Er 137.It Bq Er EINVAL 138.Fa flags 139contains an invalid value. 140.El 141.Sh SEE ALSO 142.Xr sh 1 , 143.Xr fork 2 , 144.Xr read 2 , 145.Xr socketpair 2 , 146.Xr write 2 147.Sh STANDARDS 148The 149.Fn pipe 150function conforms to 151.St -p1003.1-90 . 152.Sh HISTORY 153A 154.Fn pipe 155function call appeared in 156.At v6 . 157The 158.Fn pipe2 159function is inspired from Linux and appeared in 160.Nx 6.0 . 161