fork


#include "unistd.h"
#include "fcntl.h"
#include "stdio.h"

int main() {
    int fd = open("/tmp/tmp.txt", O_CREAT|O_TRUNC|O_WRONLY, 0777);
    if (fork() == 0) {
        printf("[child]  fd = %d\n", fd);
        write(fd, "child\n", 6);
    } else {
        printf("[parent] fd = %d\n", fd);
        write(fd, "parent\n", 7);
    }
}

---
fork bummer

int main() {
    printf("hello world ");
    fork();
    printf("hello again\n");
}

---
pipe

int main() {
    int fdarray[2];
    char buf[512];
    int n, pid;

    pipe(fdarray);
    pid = fork();

    if(pid > 0){
        write(fdarray[1], "hello", 5);
    } else {
        n = read(fdarray[0], buf, sizeof(buf));
        printf("%s\n", buf);
    }
}