NAME¶
pipe, pipe2 - create pipe
SYNOPSIS¶
#include <unistd.h>
int pipe(int pipefd[2]);
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <fcntl.h> /* Obtain O_* constant definitions */
#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.
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 <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);
}
}
SEE ALSO¶
fork(2),
read(2),
socketpair(2),
write(2),
popen(3),
pipe(7)
COLOPHON¶
This page is part of release 3.44 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/.