vfork-dup.c

#include <stdio.h>
#include <unistd.h>

int main() {
    int fd[2];
    int a = 0;

    pipe(fd);

    if (vfork()) {
        sleep(1);
        close(fd[0]);
        printf("[parent] Give me an a: ");
        // this should fail, as stdin has been modified by dup2
        scanf("%i", &a);
        printf("[parent] The a you gave was: %i\n", a);
    }
    else {
        close(fd[1]);
        dup2(fd[0], 0);
        execlp("echo", "echo", "[child]", NULL);
    }

    return 0;
}