demonstration of using pipe() and fork() to redirect

pipe-example.c

#define _XOPEN_SOURCE 700
#define _POSIX_C_SOURCE 200809L
#include <stdio.h>
#include <unistd.h>

int main() {
        int s, fd[2];
        pipe(fd);
        if (!fork()) { /* child */
                dup2(fd[0], STDIN_FILENO);
                close(fd[0]); // not that critical, just a waste
                close(fd[1]); // we must close() this copy that the server can close it's end point to signal that 'cat' should terminate
                printf("child pid:%d\n", getpid());
                execl("/bin/cat", "cat", NULL);
                perror("cat");
                return 1;
        } else { /* parent */
                int i;
                pid_t child;

                close(fd[0]); // not that critical, just a waste
                return 1;
        } else { /* parent */
                int i;
                pid_t child;

                close(fd[0]); // not that critical, just a waste
                for (i = 1; i <= 3; i++) {
                        dprintf(fd[1], "Counting %d ...\n", i);
                        sleep(1);
                }
                close(fd[1]); // we should expect 'cat' to terminate now
                child = wait(&s);
                if (child < 0)
                        perror("wait()");
                else
                        printf("child(%d) status:%#X\n", child, s);
        }

        printf("done!\n");

        return 0;
}