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.\"	$NetBSD: pipe.2,v 1.6 1995/02/27 12:35:27 cgd Exp $
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.\"     @(#)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[2]"
.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[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;
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 .