| 1 | .\" Copyright (c) 1980 Regents of the University of California.
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| 2 | .\" All rights reserved. The Berkeley software License Agreement
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| 3 | .\" specifies the terms and conditions for redistribution.
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| 4 | .\"
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| 5 | .\" @(#)pipe.2 6.2 (Berkeley) 8/26/85
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| 6 | .\"
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| 7 | .TH PIPE 2 "August 26, 1985"
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| 8 | .UC 4
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| 9 | .SH NAME
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| 10 | pipe \- create an interprocess communication channel
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| 11 | .SH SYNOPSIS
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| 12 | .nf
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| 13 | .ft B
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| 14 | #include <unistd.h>
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| 15 |
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| 16 | int pipe(int \fIfildes\fP[2])
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| 17 | .fi
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| 18 | .ft R
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| 19 | .SH DESCRIPTION
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| 20 | The
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| 21 | .B pipe
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| 22 | system call
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| 23 | creates an I/O mechanism called a pipe.
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| 24 | The file descriptors returned can
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| 25 | be used in read and write operations.
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| 26 | When the pipe is written using the descriptor
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| 27 | .IR fildes [1]
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| 28 | up to PIPE_MAX bytes of data are buffered
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| 29 | before the writing process is suspended.
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| 30 | A read using the descriptor
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| 31 | .IR fildes [0]
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| 32 | will pick up the data.
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| 33 | .PP
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| 34 | PIPE_MAX equals 7168 under MINIX 3, but note that most systems use 4096.
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| 35 | .PP
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| 36 | It is assumed that after the
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| 37 | pipe has been set up,
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| 38 | two (or more)
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| 39 | cooperating processes
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| 40 | (created by subsequent
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| 41 | .B fork
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| 42 | calls)
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| 43 | will pass data through the
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| 44 | pipe with
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| 45 | .B read
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| 46 | and
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| 47 | .B write
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| 48 | calls.
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| 49 | .PP
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| 50 | The shell has a syntax
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| 51 | to set up a linear array of processes
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| 52 | connected by pipes.
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| 53 | .PP
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| 54 | Read calls on an empty
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| 55 | pipe (no buffered data) with only one end
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| 56 | (all write file descriptors closed)
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| 57 | returns an end-of-file.
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| 58 | .PP
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| 59 | The signal SIGPIPE is generated if a write on a pipe with only one end
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| 60 | is attempted.
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| 61 | .SH "RETURN VALUE
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| 62 | The function value zero is returned if the
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| 63 | pipe was created; \-1 if an error occurred.
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| 64 | .SH ERRORS
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| 65 | The \fBpipe\fP call will fail if:
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| 66 | .TP 15
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| 67 | [EMFILE]
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| 68 | Too many descriptors are active.
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| 69 | .TP 15
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| 70 | [ENFILE]
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| 71 | The system file table is full.
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| 72 | .TP 15
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| 73 | [ENOSPC]
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| 74 | The pipe file system (usually the root file system) has no free inodes.
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| 75 | .TP 15
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| 76 | [EFAULT]
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| 77 | The \fIfildes\fP buffer is in an invalid area of the process's address
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| 78 | space.
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| 79 | .SH "SEE ALSO"
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| 80 | .BR sh (1),
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| 81 | .BR read (2),
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| 82 | .BR write (2),
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| 83 | .BR fork (2).
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| 84 | .SH NOTES
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| 85 | Writes may return ENOSPC errors if no pipe data can be buffered, because
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| 86 | the pipe file system is full.
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| 87 | .SH BUGS
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| 88 | Should more than PIPE_MAX bytes be necessary in any
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| 89 | pipe among a loop of processes, deadlock will occur.
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