V7/usr/man/man2/pipe.2

.TH PIPE 2 
.SH NAME
pipe \- create an interprocess channel
.SH SYNOPSIS
.B pipe(fildes)
.br
.B int fildes[2];
.SH DESCRIPTION
The
.I pipe
system call
creates an I/O mechanism called a pipe.
The file descriptors returned can
be used in read and write operations.
When the pipe is written using the descriptor
.IR fildes [1]
up to 4096 bytes of data are buffered
before the writing process is suspended.
A read using the descriptor
.IR fildes [0]
will pick up the data.
Writes with a count of 4096 bytes or less are atomic;
no other process can intersperse data.
.PP
It is assumed that after the
pipe has been set up,
two (or more)
cooperating processes
(created by subsequent
.I fork
calls)
will pass data through the
pipe with
.I read
and
.I write
calls.
.PP
The Shell has a syntax
to set up a linear array of processes
connected by pipes.
.PP
Read calls on an empty
pipe (no buffered data) with only one end
(all write file descriptors closed)
returns an end-of-file.
.SH "SEE ALSO"
sh(1), read(2), write(2), fork(2)
.SH DIAGNOSTICS
The function value zero is returned if the
pipe was created; \-1 if
too many files are already open.
A signal is generated if a write on a pipe with only one end is attempted.
.SH BUGS
Should more than 4096 bytes be necessary in any
pipe among a loop of processes, deadlock will occur.
.SH ASSEMBLER
(pipe = 42.)
.br
.B sys pipe
.br
(read file descriptor in r0)
.br
(write file descriptor in r1)