157 lines
4.2 KiB
Groff
157 lines
4.2 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)pipe.2 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd May 1, 2013
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.Dt PIPE 2
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.Os
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.Sh NAME
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.Nm pipe ,
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.Nm pipe2
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.Nd create descriptor pair for interprocess communication
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn pipe "int fildes[2]"
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.Ft int
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.Fn pipe2 "int fildes[2]" "int flags"
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.Sh DESCRIPTION
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The
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.Fn pipe
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system call
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creates a
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.Em pipe ,
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which is an object allowing
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bidirectional data flow,
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and allocates a pair of file descriptors.
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.Pp
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The
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.Fn pipe2
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system call allows control over the attributes of the file descriptors
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via the
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.Fa flags
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argument.
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Values for
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.Fa flags
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are constructed by a bitwise-inclusive OR of flags from the following
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list, defined in
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.In fcntl.h :
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.Bl -tag -width ".Dv O_NONBLOCK"
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.It Dv O_CLOEXEC
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Set the close-on-exec flag for the new file descriptors.
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.It Dv O_NONBLOCK
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Set the non-blocking flag for the ends of the pipe.
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.El
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.Pp
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If the
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.Fa flags
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argument is 0, the behavior is identical to a call to
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.Fn pipe .
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.Pp
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By convention, the first descriptor is normally used as the
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.Em read end
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of the pipe,
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and the second is normally the
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.Em write end ,
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so that data written to
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.Fa fildes[1]
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appears on (i.e., can be read from)
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.Fa fildes[0] .
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This allows the output of one program to be
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sent
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to another program:
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the source's standard output is set up to be
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the write end of the pipe,
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and the sink's standard input is set up to be
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the read end of the pipe.
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The pipe itself persists until all its associated descriptors are
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closed.
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.Pp
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A pipe that has had an end closed is considered
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.Em widowed .
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Writing on such a pipe causes the writing process to receive
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a
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.Dv SIGPIPE
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signal.
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Widowing a pipe is the only way to deliver end-of-file to a reader:
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after the reader consumes any buffered data, reading a widowed pipe
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returns a zero count.
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.Pp
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The bidirectional nature of this implementation of pipes is not
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portable to older systems, so it is recommended to use the convention
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for using the endpoints in the traditional manner when using a
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pipe in one direction.
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.Sh RETURN VALUES
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.Rv -std pipe
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.Sh ERRORS
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The
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.Fn pipe
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and
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.Fn pipe2
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system calls will fail if:
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.Bl -tag -width Er
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.It Bq Er EMFILE
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Too many descriptors are active.
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.It Bq Er ENFILE
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The system file table is full.
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.It Bq Er ENOMEM
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Not enough kernel memory to establish a pipe.
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.El
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.Pp
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The
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.Fn pipe2
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system call will also fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa flags
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argument is invalid.
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.El
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.Sh SEE ALSO
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.Xr sh 1 ,
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.Xr fork 2 ,
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.Xr read 2 ,
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.Xr socketpair 2 ,
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.Xr write 2
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.Sh HISTORY
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The
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.Fn pipe
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function appeared in
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.At v3 .
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.Pp
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Bidirectional pipes were first used on
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.At V.4 .
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.Pp
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The
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.Fn pipe2
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function appeared in
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.Fx 10.0 .
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