pipe

pipe - create pipe

#include <unistd.h> I int pipe(int filedes [2]);

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

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

EFAULT

EMFILE

ENFILE

POSIX.1-2001.

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);
    }
}

fork(2), read(2), socketpair(2), write(2), popen(3), pipe(7)