#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <fcntl.h>

int main (void) {
    int fd[2];
    pid_t pid;

    if (0 != pipe(fd)) {
        fprintf (stderr, "Cannot open pipe; %s\n",
                 strerror(errno));
        exit(1);
    }

    /* fd[0] is now for reading, fd[1] for writing. */

    pid = fork();
    if (pid > 0) {
        /* Parent because pid non-zero */
        FILE *input;
        char buf[100];
        int status;

        printf("Parent speaking child pid is %d\n", (int)pid);

        close(fd[1]);           /* We don't need that anymore */

        /* For sanity craft a FILE* for fd[0] which is where we read from */
        if (NULL == (input = fdopen(fd[0], "r"))) {
            fprintf (stderr, "fdopen failed?\n");
            exit(1);
        }

        for(;;) {
            if (NULL == fgets (buf, sizeof buf, input)) {
                if (feof(input)) {
                    fprintf(stderr, "Got EOF from child\n");
                    break;
                } else {
                    fprintf(stderr, "Huh? Reading failed?\n");
                    exit(1);
                }
            }

            fprintf (stderr, "Child said: \"%s\"\n", buf);
        }

        if (waitpid(pid, &status, 0) < 0) {
            fprintf(stderr, "waitpid(2): %s\n", strerror(errno));
            exit(1);
        } else if (WIFEXITED(status)) {
            fprintf (stderr, "Child's exited with status %d\n", WEXITSTATUS(status));
        } else {
            fprintf (stderr, "um, something else happened to child (0x%x)\n", status);
        }
        exit(0);
    } else if (pid == 0) {
        /* Child */
        /* Get rid of fd[0], as we don't need it */
        close(fd[0]);
        /* Close our stdin, stdout, keep stderr though */
        close(0);               /* stdin */
        close(1);               /* stdout */
        
        /* FDs will be allocated from the least numbered free fd, that is in order 0, 1 */

        /* Craft new fd 0 = stdin */
        if (open("/dev/null", O_RDONLY) != 0) {
            fprintf(stderr, "No /dev/null for us? %s\n",
                    strerror(errno));
            exit(1);
        }

        /* Make our pipe writing end fd 1 = stdout */
        dup(fd[1]);
        close(fd[1]);

        /* Exec process */
        execlp("/bin/date", "date", NULL);

        fprintf(stderr, "We survived. exec(2) failed; %s\n",
                strerror(errno));
        exit(1);
    } else {
        fprintf(stderr, "fork(2) failed; %s\n",
                strerror(errno));
    }

    return 0;
}