1.\" $NetBSD: pipe.2,v 1.29 2013/04/23 23:39:13 elric 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.Ft int 45.Fn pipe2 "int fildes[2]" "int flags" 46.Sh DESCRIPTION 47The 48.Fn pipe 49function 50creates a 51.Em pipe , 52which is an object allowing 53unidirectional data flow, 54and allocates a pair of file descriptors. 55The first descriptor connects to the 56.Em read end 57of the pipe, 58and the second connects to the 59.Em write end , 60so that data written to 61.Fa fildes[1] 62appears on (i.e., can be read from) 63.Fa fildes[0] . 64This allows the output of one program to be 65sent 66to another program: 67the source's standard output is set up to be 68the write end of the pipe, 69and the sink's standard input is set up to be 70the read end of the pipe. 71The pipe itself persists until all its associated descriptors are 72closed. 73.Pp 74A pipe whose read or write end has been closed is considered 75.Em widowed . 76Writing on such a pipe causes the writing process to receive 77a 78.Dv SIGPIPE 79signal. 80Widowing a pipe is the only way to deliver end-of-file to a reader: 81after the reader consumes any buffered data, reading a widowed pipe 82returns a zero count. 83.Pp 84The 85.Fn pipe2 86function 87behaves exactly like 88.Fn pipe 89only it allows extra 90.Fa flags 91to be set on the returned file descriptor. 92The following flags are valid: 93.Bl -tag -width O_NONBLOCK -offset indent 94.It Dv O_CLOEXEC 95Set the 96.Dq close-on-exec 97property. 98.It Dv O_NONBLOCK 99Sets non-blocking I/O. 100.It Dv O_NOSIGPIPE 101Return 102.Er EPIPE 103instead of raising 104.Dv SIGPIPE . 105.El 106.Sh RETURN VALUES 107On successful creation of the pipe, zero is returned. 108Otherwise, a value of \-1 is returned and the variable 109.Va errno 110set to indicate the 111error. 112.Sh ERRORS 113The 114.Fn pipe 115and 116.Fn pipe2 117calls will fail if: 118.Bl -tag -width Er 119.It Bq Er EFAULT 120The 121.Fa fildes 122buffer is in an invalid area of the process's address space. 123The reliable detection of this error cannot be guaranteed; when not 124detected, a signal may be delivered to the process, indicating an 125address violation. 126.It Bq Er EMFILE 127Too many descriptors are active. 128.It Bq Er ENFILE 129The system file table is full. 130.El 131.Pp 132.Fn pipe2 133will also fail if: 134.Bl -tag -width Er 135.It Bq Er EINVAL 136.Fa flags 137is other than 138.Dv O_NONBLOCK , 139.Dv O_NOSIGPIPE 140or 141.Dv O_CLOEXEC . 142.El 143.Sh SEE ALSO 144.Xr sh 1 , 145.Xr fork 2 , 146.Xr read 2 , 147.Xr socketpair 2 , 148.Xr write 2 149.Sh STANDARDS 150The 151.Fn pipe 152function conforms to 153.St -p1003.1-90 . 154.Sh HISTORY 155A 156.Fn pipe 157function call appeared in 158.At v6 . 159The 160.Fn pipe2 161function is inspired from Linux and appeared in 162.Nx 6.0 . 163