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+.\" 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.
+.\" 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
+.\" $FreeBSD$
+.\"
+.Dd January 30, 2006
+.Dt PIPE 2
+.Os
+.Sh NAME
+.Nm pipe
+.Nd create descriptor pair for interprocess communication
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In unistd.h
+.Ft int
+.Fn pipe "int fildes[2]"
+.Sh DESCRIPTION
+The
+.Fn pipe
+system call
+creates a
+.Em pipe ,
+which is an object allowing
+bidirectional data flow,
+and allocates a pair of file descriptors.
+.Pp
+By convention, the first descriptor is normally used as the
+.Em read end
+of the pipe,
+and the second is normally the
+.Em write end ,
+so that data written to
+.Fa fildes[1]
+appears on (i.e., can be read from)
+.Fa fildes[0] .
+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,
+and the sink's standard input is set up to be
+the read end of the pipe.
+The pipe itself persists until all its associated descriptors are
+closed.
+.Pp
+A pipe that has had an end 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.
+.Pp
+The bidirectional nature of this implementation of pipes is not
+portable to older systems, so it is recommended to use the convention
+for using the endpoints in the traditional manner when using a
+pipe in one direction.
+.Sh RETURN VALUES
+.Rv -std pipe
+.Sh ERRORS
+The
+.Fn pipe
+system call will fail if:
+.Bl -tag -width Er
+.It Bq Er EMFILE
+Too many descriptors are active.
+.It Bq Er ENFILE
+The system file table is full.
+.It Bq Er ENOMEM
+Not enough kernel memory to establish a pipe.
+.El
+.Sh SEE ALSO
+.Xr sh 1 ,
+.Xr fork 2 ,
+.Xr read 2 ,
+.Xr socketpair 2 ,
+.Xr write 2
+.Sh HISTORY
+The
+.Fn pipe
+function appeared in
+.At v3 .
+.Pp
+Bidirectional pipes were first used on
+.At V.4 .