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PIPE(2) Linux Programmer's Manual PIPE(2)
pipe, pipe2 - create pipe
#include <unistd.h>
int pipe(int pipefd[2]);
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <unistd.h>
int pipe2(int pipefd[2], int flags);
pipe() creates a pipe, a unidirectional data channel that can be used for
interprocess communication. The array pipefd is used to return two file
descriptors referring to the ends of the pipe. pipefd[0] refers to the read
end of the pipe. pipefd[1] refers to the write end of the pipe. Data written
to the write end of the pipe is buffered by the kernel until it is read from
the read end of the pipe. For further details, see pipe(7).
If flags is 0, then pipe2() is the same as pipe(). The following values can
be bitwise ORed in flags to obtain different behavior:
O_NONBLOCK Set the O_NONBLOCK file status flag on the two new open file
descriptions. Using this flag saves extra calls to fcntl(2) to
achieve the same result.
O_CLOEXEC Set the close-on-exec (FD_CLOEXEC) flag on the two new file
descriptors. See the description of the same flag in open(2) for
reasons why this may be useful.
On success, zero is returned. On error, -1 is returned, and errno is set
appropriately.
EFAULT pipefd is not valid.
EINVAL (pipe2()) Invalid value in flags.
EMFILE Too many file descriptors are in use by the process.
ENFILE The system limit on the total number of open files has been reached.
pipe2() was added to Linux in version 2.6.27; glibc support is available
starting with version 2.9.
pipe(): POSIX.1-2001.
pipe2() is Linux-specific.
The following program creates a pipe, and then fork(2)s to create a child
process; the child inherits a duplicate set of file descriptors that refer to
the same pipe. After the fork(2), each process closes the descriptors that it
doesn't need for the pipe (see pipe(7)). The parent then writes the string
contained in the program's command-line argument to the pipe, and the child
reads this string a byte at a time from the pipe and echoes it on standard
output.
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int
main(int argc, char *argv[])
{
int pipefd[2];
pid_t cpid;
char buf;
if (argc != 2) {
fprintf(stderr, "Usage: %s <string>\n", argv[0]);
exit(EXIT_FAILURE);
}
if (pipe(pipefd) == -1) {
perror("pipe");
exit(EXIT_FAILURE);
}
cpid = fork();
if (cpid == -1) {
perror("fork");
exit(EXIT_FAILURE);
}
if (cpid == 0) { /* Child reads from pipe */
close(pipefd[1]); /* Close unused write end */
while (read(pipefd[0], &buf, 1) > 0)
write(STDOUT_FILENO, &buf, 1);
write(STDOUT_FILENO, "\n", 1);
close(pipefd[0]);
_exit(EXIT_SUCCESS);
} else { /* Parent writes argv[1] to pipe */
close(pipefd[0]); /* Close unused read end */
write(pipefd[1], argv[1], strlen(argv[1]));
close(pipefd[1]); /* Reader will see EOF */
wait(NULL); /* Wait for child */
exit(EXIT_SUCCESS);
}
}
fork(2), read(2), socketpair(2), write(2), popen(3), pipe(7)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2010-09-10 PIPE(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface