PIPE(2)

NAME
pipe - create pipe

SYNOPSIS
#include <unistd.h>

int pipe(int filedes[2]);

DESCRIPTION
pipe() creates a pair of file descriptors, pointing to a pipe inode, and places them in the array pointed to by filedes. filedes[0] is for reading, filedes[1] is for writing.

RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EFAULT
    filedes is not valid.

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.

CONFORMING TO
POSIX.1-2001.

EXAMPLE
The following program creates a pipe, and then fork(2)s to create a child process. 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 pfd[2];
    pid_t cpid;
    char buf;

    assert(argc == 2);

    if (pipe(pfd) == -1) { perror("pipe"); exit(EXIT_FAILURE); }

    cpid = fork();
    if (cpid == -1) { perror("fork"); exit(EXIT_FAILURE); }

    if (cpid == 0) {    /* Child reads from pipe */
        close(pfd[1]);          /* Close unused write end */

        while (read(pfd[0], &buf, 1) > 0)
            write(STDOUT_FILENO, &buf, 1);

        write(STDOUT_FILENO, "\n", 1);
        close(pfd[0]);
        _exit(EXIT_SUCCESS);

    } else {            /* Parent writes argv[1] to pipe */
        close(pfd[0]);          /* Close unused read end */
        write(pfd[1], argv[1], strlen(argv[1]));
        close(pfd[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)