#include <unistd.h>int pipe(int pipefd[2]);#define _GNU_SOURCE#include <unistd.h>int pipe2(int pipefd[2], int flags);
DESCRIPTION
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.
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
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.
VERSIONS
pipe2()
was added to Linux in version 2.6.27;
glibc support is available starting with
version 2.9.
CONFORMING TO
pipe():
POSIX.1-2001.
pipe2()
is Linux-specific.
EXAMPLE
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 <assert.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;
assert(argc == 2);
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);
}
}
This page is part of release 3.14 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/.
