2005-05-02 15:01:42 +02:00
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.\" Copyright (c) 1980 Regents of the University of California.
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.\" All rights reserved. The Berkeley software License Agreement
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.\" specifies the terms and conditions for redistribution.
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.\"
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.\" @(#)pipe.2 6.2 (Berkeley) 8/26/85
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.\"
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.TH PIPE 2 "August 26, 1985"
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.UC 4
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.SH NAME
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pipe \- create an interprocess communication channel
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.SH SYNOPSIS
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.nf
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.ft B
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#include <unistd.h>
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int pipe(int \fIfildes\fP[2])
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.fi
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.ft R
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.SH DESCRIPTION
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The
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.B pipe
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system call
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creates an I/O mechanism called a pipe.
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The file descriptors returned can
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be used in read and write operations.
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When the pipe is written using the descriptor
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.IR fildes [1]
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up to PIPE_MAX bytes of data are buffered
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before the writing process is suspended.
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A read using the descriptor
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.IR fildes [0]
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will pick up the data.
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.PP
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2005-08-22 14:56:02 +02:00
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PIPE_MAX equals 7168 under MINIX 3, but note that most systems use 4096.
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2005-05-02 15:01:42 +02:00
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.PP
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It is assumed that after the
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pipe has been set up,
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two (or more)
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cooperating processes
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(created by subsequent
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.B fork
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calls)
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will pass data through the
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pipe with
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.B read
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and
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.B write
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calls.
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.PP
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The shell has a syntax
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to set up a linear array of processes
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connected by pipes.
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.PP
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Read calls on an empty
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pipe (no buffered data) with only one end
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(all write file descriptors closed)
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returns an end-of-file.
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.PP
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The signal SIGPIPE is generated if a write on a pipe with only one end
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is attempted.
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.SH "RETURN VALUE
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The function value zero is returned if the
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pipe was created; \-1 if an error occurred.
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.SH ERRORS
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The \fBpipe\fP call will fail if:
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.TP 15
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[EMFILE]
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Too many descriptors are active.
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.TP 15
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[ENFILE]
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The system file table is full.
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.TP 15
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[ENOSPC]
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The pipe file system (usually the root file system) has no free inodes.
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.TP 15
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[EFAULT]
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The \fIfildes\fP buffer is in an invalid area of the process's address
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space.
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.SH "SEE ALSO"
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.BR sh (1),
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.BR read (2),
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.BR write (2),
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.BR fork (2).
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.SH NOTES
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Writes may return ENOSPC errors if no pipe data can be buffered, because
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the pipe file system is full.
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.SH BUGS
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Should more than PIPE_MAX bytes be necessary in any
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pipe among a loop of processes, deadlock will occur.
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