1 .\" Copyright (C) 2005, 2008, Michael Kerrisk <mtk.manpages@gmail.com>
2 .\" (A few fragments remain from an earlier (1992) version by
3 .\" Drew Eckhardt <drew@cs.colorado.edu>.)
5 .\" %%%LICENSE_START(VERBATIM)
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12 .\" entire resulting derived work is distributed under the terms of a
13 .\" permission notice identical to this one.
15 .\" Since the Linux kernel and libraries are constantly changing, this
16 .\" manual page may be incorrect or out-of-date. The author(s) assume no
17 .\" responsibility for errors or omissions, or for damages resulting from
18 .\" the use of the information contained herein. The author(s) may not
19 .\" have taken the same level of care in the production of this manual,
20 .\" which is licensed free of charge, as they might when working
23 .\" Formatted or processed versions of this manual, if unaccompanied by
24 .\" the source, must acknowledge the copyright and authors of this work.
27 .\" Modified by Michael Haardt <michael@moria.de>
28 .\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
29 .\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
30 .\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
31 .\" Modified 2005, mtk: added an example program
32 .\" Modified 2008-01-09, mtk: rewrote DESCRIPTION; minor additions
34 .\" 2008-10-10, mtk: add description of pipe2()
36 .TH PIPE 2 2014-02-11 "Linux" "Linux Programmer's Manual"
38 pipe, pipe2 \- create pipe
41 .B #include <unistd.h>
43 .BI "int pipe(int " pipefd "[2]);"
45 .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
46 .BR "#include <fcntl.h>" " /* Obtain O_* constant definitions */
47 .B #include <unistd.h>
49 .BI "int pipe2(int " pipefd "[2], int " flags );
53 creates a pipe, a unidirectional data channel that
54 can be used for interprocess communication.
57 is used to return two file descriptors referring to the ends of the pipe.
59 refers to the read end of the pipe.
61 refers to the write end of the pipe.
62 Data written to the write end of the pipe is buffered by the kernel
63 until it is read from the read end of the pipe.
64 For further details, see
73 The following values can be bitwise ORed in
75 to obtain different behavior:
80 flag on the two new file descriptors.
81 See the description of the same flag in
83 for reasons why this may be useful.
85 .BR O_DIRECT " (since Linux 3.4)"
86 .\" commit 9883035ae7edef3ec62ad215611cb8e17d6a1a5d
87 Create a pipe that performs I/O in "packet" mode.
90 to the pipe is dealt with as a separate packet, and
92 from the pipe will read one packet at a time.
93 Note the following points:
96 Writes of greater than
100 will be split into multiple packets.
104 specifies a buffer size that is smaller than the next packet,
105 then the requested number of bytes are read,
106 and the excess bytes in the packet are discarded.
107 Specifying a buffer size of
109 will be sufficient to read the largest possible packets
110 (see the previous point).
112 Zero-length packets are not supported.
115 that specifies a buffer size of zero is a no-op, and returns 0.)
118 Older kernels that do not support this flag will indicate this via an
125 file status flag on the two new open file descriptions.
126 Using this flag saves extra calls to
128 to achieve the same result.
130 On success, zero is returned.
131 On error, \-1 is returned, and
133 is set appropriately.
146 Too many file descriptors are in use by the process.
149 The system limit on the total number of open files has been reached.
152 was added to Linux in version 2.6.27;
153 glibc support is available starting with
162 .\" fork.2 refers to this example program.
163 The following program creates a pipe, and then
165 to create a child process;
166 the child inherits a duplicate set of file
167 descriptors that refer to the same pipe.
170 each process closes the descriptors that it doesn't need for the pipe
173 The parent then writes the string contained in the program's
174 command-line argument to the pipe,
175 and the child reads this string a byte at a time from the pipe
176 and echoes it on standard output.
179 #include <sys/types.h>
180 #include <sys/wait.h>
187 main(int argc, char *argv[])
194 fprintf(stderr, "Usage: %s <string>\\n", argv[0]);
198 if (pipe(pipefd) == \-1) {
209 if (cpid == 0) { /* Child reads from pipe */
210 close(pipefd[1]); /* Close unused write end */
212 while (read(pipefd[0], &buf, 1) > 0)
213 write(STDOUT_FILENO, &buf, 1);
215 write(STDOUT_FILENO, "\\n", 1);
219 } else { /* Parent writes argv[1] to pipe */
220 close(pipefd[0]); /* Close unused read end */
221 write(pipefd[1], argv[1], strlen(argv[1]));
222 close(pipefd[1]); /* Reader will see EOF */
223 wait(NULL); /* Wait for child */
236 This page is part of release 3.67 of the Linux
239 A description of the project,
240 information about reporting bugs,
241 and the latest version of this page,
243 \%http://www.kernel.org/doc/man\-pages/.