1 .\" Hey Emacs! This file is -*- nroff -*- source.
3 .\" Copyright (C) 2005, 2008, Michael Kerrisk <mtk.manpages@gmail.com>
4 .\" (A few fragments remain from an earlier (1992) version by
5 .\" Drew Eckhardt <drew@cs.colorado.edu>.)
7 .\" Permission is granted to make and distribute verbatim copies of this
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11 .\" Permission is granted to copy and distribute modified versions of this
12 .\" manual under the conditions for verbatim copying, provided that the
13 .\" entire resulting derived work is distributed under the terms of a
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16 .\" Since the Linux kernel and libraries are constantly changing, this
17 .\" manual page may be incorrect or out-of-date. The author(s) assume no
18 .\" responsibility for errors or omissions, or for damages resulting from
19 .\" the use of the information contained herein. The author(s) may not
20 .\" have taken the same level of care in the production of this manual,
21 .\" which is licensed free of charge, as they might when working
24 .\" Formatted or processed versions of this manual, if unaccompanied by
25 .\" 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 2012-02-14 "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 file status flag on the two new open file descriptions.
81 Using this flag saves extra calls to
83 to achieve the same result.
88 flag on the two new file descriptors.
89 See the description of the same flag in
91 for reasons why this may be useful.
93 On success, zero is returned.
94 On error, \-1 is returned, and
109 Too many file descriptors are in use by the process.
112 The system limit on the total number of open files has been reached.
115 was added to Linux in version 2.6.27;
116 glibc support is available starting with
125 .\" fork.2 refers to this example program.
126 The following program creates a pipe, and then
128 to create a child process;
129 the child inherits a duplicate set of file
130 descriptors that refer to the same pipe.
133 each process closes the descriptors that it doesn't need for the pipe
136 The parent then writes the string contained in the program's
137 command-line argument to the pipe,
138 and the child reads this string a byte at a time from the pipe
139 and echoes it on standard output.
142 #include <sys/wait.h>
149 main(int argc, char *argv[])
156 fprintf(stderr, "Usage: %s <string>\\n", argv[0]);
160 if (pipe(pipefd) == \-1) {
171 if (cpid == 0) { /* Child reads from pipe */
172 close(pipefd[1]); /* Close unused write end */
174 while (read(pipefd[0], &buf, 1) > 0)
175 write(STDOUT_FILENO, &buf, 1);
177 write(STDOUT_FILENO, "\\n", 1);
181 } else { /* Parent writes argv[1] to pipe */
182 close(pipefd[0]); /* Close unused read end */
183 write(pipefd[1], argv[1], strlen(argv[1]));
184 close(pipefd[1]); /* Reader will see EOF */
185 wait(NULL); /* Wait for child */