PIPE(2) Linux Programmer's Manual PIPE(2)NAME
pipe, pipe2 - create pipe
SYNOPSIS
#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);
DESCRIPTIONpipe() 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 val‐
ues 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.
VERSIONSpipe2() was added to Linux in version 2.6.27; glibc support is avail‐
able starting with version 2.9.
CONFORMING TOpipe(): 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 ALSOfork(2), read(2), socketpair(2), write(2), popen(3), pipe(7)COLOPHON
This page is part of release 3.35 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://man7.org/linux/man-pages/.
Linux 2010-09-10 PIPE(2)
