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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10 .\" Permission is granted to copy and distribute modified versions of this
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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16 .\" manual page may be incorrect or out-of-date.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 2014-07-08 "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.
108 specifies a buffer size that is smaller than the next packet,
109 then the requested number of bytes are read,
110 and the excess bytes in the packet are discarded.
111 Specifying a buffer size of
113 will be sufficient to read the largest possible packets
114 (see the previous point).
116 Zero-length packets are not supported.
119 that specifies a buffer size of zero is a no-op, and returns 0.)
122 Older kernels that do not support this flag will indicate this via an
129 file status flag on the two new open file descriptions.
130 Using this flag saves extra calls to
132 to achieve the same result.
134 On success, zero is returned.
135 On error, \-1 is returned, and
137 is set appropriately.
150 Too many file descriptors are in use by the process.
153 The system limit on the total number of open files has been reached.
156 was added to Linux in version 2.6.27;
157 glibc support is available starting with
166 .\" fork.2 refers to this example program.
167 The following program creates a pipe, and then
169 to create a child process;
170 the child inherits a duplicate set of file
171 descriptors that refer to the same pipe.
174 each process closes the descriptors that it doesn't need for the pipe
177 The parent then writes the string contained in the program's
178 command-line argument to the pipe,
179 and the child reads this string a byte at a time from the pipe
180 and echoes it on standard output.
183 #include <sys/types.h>
184 #include <sys/wait.h>
191 main(int argc, char *argv[])
198 fprintf(stderr, "Usage: %s <string>\\n", argv[0]);
202 if (pipe(pipefd) == \-1) {
213 if (cpid == 0) { /* Child reads from pipe */
214 close(pipefd[1]); /* Close unused write end */
216 while (read(pipefd[0], &buf, 1) > 0)
217 write(STDOUT_FILENO, &buf, 1);
219 write(STDOUT_FILENO, "\\n", 1);
223 } else { /* Parent writes argv[1] to pipe */
224 close(pipefd[0]); /* Close unused read end */
225 write(pipefd[1], argv[1], strlen(argv[1]));
226 close(pipefd[1]); /* Reader will see EOF */
227 wait(NULL); /* Wait for child */
240 This page is part of release 3.79 of the Linux
243 A description of the project,
244 information about reporting bugs,
245 and the latest version of this page,
247 \%http://www.kernel.org/doc/man\-pages/.