#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
int main() {
   int pipefd[2], child_pid, grand_child;

   pipe(pipefd);

   child_pid = fork();

   if (child_pid) {
      waitpid(child_pid, NULL, 0);
      /* Parent */

      grand_child = fork();

      if (!grand_child) {
         dup2(pipefd[0], STDIN_FILENO);
         close(pipefd[0]);
         close(pipefd[1]);
         execlp("cat", "cat", NULL);
      } else {
         waitpid(grand_child, NULL, 0);
      }

   } else {
      /* Child */

      dup2(pipefd[1], STDOUT_FILENO);

      close(pipefd[1]);
      close(pipefd[0]);


      execlp("ls", "ls", NULL);
   }

   return 0;
}