.\" $NetBSD: pipe.2,v 1.6 1995/02/27 12:35:27 cgd Exp $ .\" .\" Copyright (c) 1980, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)pipe.2 8.1 (Berkeley) 6/4/93 .\" .Dd June 4, 1993 .Dt PIPE 2 .Os BSD 4 .Sh NAME .Nm pipe .Nd create descriptor pair for interprocess communication .Sh SYNOPSIS .Fd #include <unistd.h> .Ft int .Fo pipe .Fa "int fildes" .Fc .Sh DESCRIPTION The .Fn pipe function creates a .Em pipe (an object that allows unidirectional data flow) and allocates a pair of file descriptors. The first descriptor connects to the .Em read end of the pipe; the second connects to the .Em write end . .Pp Data written to .Fa fildes appears on (i.e., can be read from) .Fa fildes . This allows the output of one program to be sent to another program: the source's standard output is set up to be the write end of the pipe; the sink's standard input is set up to be the read end of the pipe. The pipe itself persists until all of its associated descriptors are closed. .Pp A pipe whose read or write end has been closed is considered .Em widowed . Writing on such a pipe causes the writing process to receive a .Dv SIGPIPE signal. Widowing a pipe is the only way to deliver end-of-file to a reader: after the reader consumes any buffered data, reading a widowed pipe returns a zero count. .Sh RETURN VALUES On successful creation of the pipe, zero is returned. Otherwise, a value of -1 is returned and the variable .Va errno set to indicate the error. .Sh ERRORS The .Fn pipe call will fail if: .Bl -tag -width Er .\" =========== .It Bq Er EFAULT The .Fa fildes buffer is in an invalid area of the process's address space. .\" =========== .It Bq Er EMFILE Too many descriptors are active. .\" =========== .It Bq Er ENFILE The system file table is full. .El .Sh SEE ALSO .Xr sh 1 , .Xr fork 2 , .Xr read 2 , .Xr socketpair 2 , .Xr write 2 .Sh HISTORY A .Fn pipe function call appeared in .At v6 .