1PIPE(2) Linux Programmer's Manual PIPE(2)
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6 pipe, pipe2 - create pipe
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9 #include <unistd.h>
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11 int pipe(int pipefd[2]);
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13 #define _GNU_SOURCE
14 #include <unistd.h>
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16 int pipe2(int pipefd[2], int flags);
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19 pipe() creates a pipe, a unidirectional data channel that can be used
20 for interprocess communication. The array pipefd is used to return two
21 file descriptors referring to the ends of the pipe. pipefd[0] refers
22 to the read end of the pipe. pipefd[1] refers to the write end of the
23 pipe. Data written to the write end of the pipe is buffered by the
24 kernel until it is read from the read end of the pipe. For further
25 details, see pipe(7).
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27 If flags is 0, then pipe2() is the same as pipe(). The following val‐
28 ues can be bitwise ORed in flags to obtain different behavior:
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30 O_NONBLOCK Set the O_NONBLOCK file status flag on the two new open
31 file descriptions. Using this flag saves extra calls to
32 fcntl(2) to achieve the same result.
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34 O_CLOEXEC Set the close-on-exec (FD_CLOEXEC) flag on the two new file
35 descriptors. See the description of the same flag in
36 open(2) for reasons why this may be useful.
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39 On success, zero is returned. On error, -1 is returned, and errno is
40 set appropriately.
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43 EFAULT pipefd is not valid.
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45 EINVAL (pipe2()) Invalid value in flags.
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47 EMFILE Too many file descriptors are in use by the process.
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49 ENFILE The system limit on the total number of open files has been
50 reached.
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53 pipe2() was added to Linux in version 2.6.27; glibc support is avail‐
54 able starting with version 2.9.
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57 pipe(): POSIX.1-2001.
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59 pipe2() is Linux-specific.
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62 The following program creates a pipe, and then fork(2)s to create a
63 child process; the child inherits a duplicate set of file descriptors
64 that refer to the same pipe. After the fork(2), each process closes
65 the descriptors that it doesn't need for the pipe (see pipe(7)). The
66 parent then writes the string contained in the program's command-line
67 argument to the pipe, and the child reads this string a byte at a time
68 from the pipe and echoes it on standard output.
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70 #include <sys/wait.h>
71 #include <assert.h>
72 #include <stdio.h>
73 #include <stdlib.h>
74 #include <unistd.h>
75 #include <string.h>
76
77 int
78 main(int argc, char *argv[])
79 {
80 int pipefd[2];
81 pid_t cpid;
82 char buf;
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84 assert(argc == 2);
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86 if (pipe(pipefd) == -1) {
87 perror("pipe");
88 exit(EXIT_FAILURE);
89 }
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91 cpid = fork();
92 if (cpid == -1) {
93 perror("fork");
94 exit(EXIT_FAILURE);
95 }
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97 if (cpid == 0) { /* Child reads from pipe */
98 close(pipefd[1]); /* Close unused write end */
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100 while (read(pipefd[0], &buf, 1) > 0)
101 write(STDOUT_FILENO, &buf, 1);
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103 write(STDOUT_FILENO, "\n", 1);
104 close(pipefd[0]);
105 _exit(EXIT_SUCCESS);
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107 } else { /* Parent writes argv[1] to pipe */
108 close(pipefd[0]); /* Close unused read end */
109 write(pipefd[1], argv[1], strlen(argv[1]));
110 close(pipefd[1]); /* Reader will see EOF */
111 wait(NULL); /* Wait for child */
112 exit(EXIT_SUCCESS);
113 }
114 }
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117 fork(2), read(2), socketpair(2), write(2), popen(3), pipe(7)
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120 This page is part of release 3.22 of the Linux man-pages project. A
121 description of the project, and information about reporting bugs, can
122 be found at http://www.kernel.org/doc/man-pages/.
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126Linux 2008-11-04 PIPE(2)