1.\" Copyright (c) 1980, 1991 Regents of the University of California. 2.\" 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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)pipe.2 6.3 (Berkeley) 3/10/91 33.\" 34.Dd March 10, 1991 35.Dt PIPE 2 36.Os BSD 4 37.Sh NAME 38.Nm pipe 39.Nd create descriptor pair for interprocess communication 40.Sh SYNOPSIS 41.Fd #include <unistd.h> 42.Ft int 43.Fn pipe "int *fildes" 44.Sh DESCRIPTION 45The 46.Fn pipe 47function 48creates a 49.Em pipe , 50which is an object allowing 51unidirectional data flow, 52and allocates a pair of file descriptors. 53The first descriptor connects to the 54.Em read end 55of the pipe, 56and the second connects to the 57.Em write end , 58so that data written to 59.Fa fildes[1] 60appears on (i.e., can be read from) 61.Fa fildes[0] . 62This allows the output of one program to be 63sent 64to another program: 65the source's standard output is set up to be 66the write end of the pipe, 67and the sink's standard input is set up to be 68the read end of the pipe. 69The pipe itself persists until all its associated descriptors are 70closed. 71.Pp 72A pipe whose read or write end has been closed is considered 73.Em widowed . 74Writing on such a pipe causes the writing process to receive 75a 76.Dv SIGPIPE 77signal. 78Widowing a pipe is the only way to deliver end-of-file to a reader: 79after the reader consumes any buffered data, reading a widowed pipe 80returns a zero count. 81.Pp 82Pipes are really a special case of the 83.Xr socketpair 2 84call and, in fact, are implemented as such in the system. 85.Sh RETURN VALUES 86On successful creation of the pipe, zero is returned. Otherwise, 87a 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 [EMFILE] 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 104space. 105.El 106.Sh SEE ALSO 107.Xr sh 1 , 108.Xr read 2 , 109.Xr write 2 , 110.Xr fork 2 , 111.Xr socketpair 2 112.Sh HISTORY 113A 114.Nm 115function call appeared in Version 6 AT&T UNIX. 116