90 lines
2 KiB
Groff
90 lines
2 KiB
Groff
|
.\" Copyright (c) 1980 Regents of the University of California.
|
||
|
|
.\" All rights reserved. The Berkeley software License Agreement
|
||
|
|
.\" specifies the terms and conditions for redistribution.
|
||
|
|
.\"
|
||
|
|
.\" @(#)pipe.2 6.2 (Berkeley) 8/26/85
|
||
|
|
.\"
|
||
|
|
.TH PIPE 2 "August 26, 1985"
|
||
|
|
.UC 4
|
||
|
|
.SH NAME
|
||
|
|
pipe \- create an interprocess communication channel
|
||
|
|
.SH SYNOPSIS
|
||
|
|
.nf
|
||
|
|
.ft B
|
||
|
|
#include <unistd.h>
|
||
|
|
|
||
|
|
int pipe(int \fIfildes\fP[2])
|
||
|
|
.fi
|
||
|
|
.ft R
|
||
|
|
.SH DESCRIPTION
|
||
|
|
The
|
||
|
|
.B 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 PIPE_MAX bytes of data are buffered
|
||
|
|
before the writing process is suspended.
|
||
|
|
A read using the descriptor
|
||
|
|
.IR fildes [0]
|
||
|
|
will pick up the data.
|
||
|
|
.PP
|
||
|
|
PIPE_MAX equals 7168 under Minix, but note that most systems use 4096.
|
||
|
|
.PP
|
||
|
|
It is assumed that after the
|
||
|
|
pipe has been set up,
|
||
|
|
two (or more)
|
||
|
|
cooperating processes
|
||
|
|
(created by subsequent
|
||
|
|
.B fork
|
||
|
|
calls)
|
||
|
|
will pass data through the
|
||
|
|
pipe with
|
||
|
|
.B read
|
||
|
|
and
|
||
|
|
.B 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.
|
||
|
|
.PP
|
||
|
|
The signal SIGPIPE is generated if a write on a pipe with only one end
|
||
|
|
is attempted.
|
||
|
|
.SH "RETURN VALUE
|
||
|
|
The function value zero is returned if the
|
||
|
|
pipe was created; \-1 if an error occurred.
|
||
|
|
.SH ERRORS
|
||
|
|
The \fBpipe\fP call will fail if:
|
||
|
|
.TP 15
|
||
|
|
[EMFILE]
|
||
|
|
Too many descriptors are active.
|
||
|
|
.TP 15
|
||
|
|
[ENFILE]
|
||
|
|
The system file table is full.
|
||
|
|
.TP 15
|
||
|
|
[ENOSPC]
|
||
|
|
The pipe file system (usually the root file system) has no free inodes.
|
||
|
|
.TP 15
|
||
|
|
[EFAULT]
|
||
|
|
The \fIfildes\fP buffer is in an invalid area of the process's address
|
||
|
|
space.
|
||
|
|
.SH "SEE ALSO"
|
||
|
|
.BR sh (1),
|
||
|
|
.BR read (2),
|
||
|
|
.BR write (2),
|
||
|
|
.BR fork (2).
|
||
|
|
.SH NOTES
|
||
|
|
Writes may return ENOSPC errors if no pipe data can be buffered, because
|
||
|
|
the pipe file system is full.
|
||
|
|
.SH BUGS
|
||
|
|
Should more than PIPE_MAX bytes be necessary in any
|
||
|
|
pipe among a loop of processes, deadlock will occur.
|