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. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.Dd December 1, 2017 29.Dt PIPE 2 30.Os 31.Sh NAME 32.Nm pipe , 33.Nm pipe2 34.Nd create descriptor pair for interprocess communication 35.Sh LIBRARY 36.Lb libc 37.Sh SYNOPSIS 38.In unistd.h 39.Ft int 40.Fn pipe "int fildes[2]" 41.Ft int 42.Fn pipe2 "int fildes[2]" "int flags" 43.Sh DESCRIPTION 44The 45.Fn pipe 46function 47creates a 48.Em pipe , 49which is an object allowing 50bidirectional data flow, 51and allocates a pair of file descriptors. 52.Pp 53The 54.Fn pipe2 55system call allows control over the attributes of the file descriptors 56via the 57.Fa flags 58argument. 59Values for 60.Fa flags 61are constructed by a bitwise-inclusive OR of flags from the following 62list, defined in 63.In fcntl.h : 64.Bl -tag -width ".Dv O_NONBLOCK" 65.It Dv O_CLOEXEC 66Set the close-on-exec flag for the new file descriptors. 67.It Dv O_NONBLOCK 68Set the non-blocking flag for the ends of the pipe. 69.El 70.Pp 71If the 72.Fa flags 73argument is 0, the behavior is identical to a call to 74.Fn pipe . 75.Pp 76By convention, the first descriptor is normally used as the 77.Em read end 78of the pipe, 79and the second is normally the 80.Em write end , 81so that data written to 82.Fa fildes[1] 83appears on (i.e., can be read from) 84.Fa fildes[0] . 85This allows the output of one program to be 86sent 87to another program: 88the source's standard output is set up to be 89the write end of the pipe, 90and the sink's standard input is set up to be 91the read end of the pipe. 92The pipe itself persists until all its associated descriptors are 93closed. 94.Pp 95A pipe that has had an end closed is considered 96.Em widowed . 97Writing on such a pipe causes the writing process to receive 98a 99.Dv SIGPIPE 100signal. 101Widowing a pipe is the only way to deliver end-of-file to a reader: 102after the reader consumes any buffered data, reading a widowed pipe 103returns a zero count. 104.Pp 105The bidirectional nature of this implementation of pipes is not 106portable to older systems, so it is recommended to use the convention 107for using the endpoints in the traditional manner when using a 108pipe in one direction. 109.Sh IMPLEMENTATION NOTES 110The 111.Fn pipe 112function calls the 113.Fn pipe2 114system call. 115As a result, system call traces such as those captured by 116.Xr dtrace 1 117or 118.Xr ktrace 1 119will show calls to 120.Fn pipe2 . 121.Sh RETURN VALUES 122.Rv -std pipe 123.Sh ERRORS 124The 125.Fn pipe 126and 127.Fn pipe2 128system calls will fail if: 129.Bl -tag -width Er 130.It Bq Er EFAULT 131.Ar fildes 132argument points to an invalid memory location. 133.It Bq Er EMFILE 134Too many descriptors are active. 135.It Bq Er ENFILE 136The system file table is full. 137.It Bq Er ENOMEM 138Not enough kernel memory to establish a pipe. 139.El 140.Pp 141The 142.Fn pipe2 143system call will also fail if: 144.Bl -tag -width Er 145.It Bq Er EINVAL 146The 147.Fa flags 148argument is invalid. 149.El 150.Sh SEE ALSO 151.Xr sh 1 , 152.Xr fork 2 , 153.Xr read 2 , 154.Xr socketpair 2 , 155.Xr write 2 156.Sh HISTORY 157The 158.Fn pipe 159function appeared in 160.At v3 . 161.Pp 162Bidirectional pipes were first used on 163.At V.4 . 164.Pp 165The 166.Fn pipe2 167function appeared in 168.Fx 10.0 . 169.Pp 170The 171.Fn pipe 172function became a wrapper around 173.Fn pipe2 174in 175.Fx 11.0 . 176