// Simple pipe example

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unistd.h>
#include <sys/types.h>
#include <string.h>
#include <sys/wait.h>

int main(void) {
   int fd[2];
   pid_t pid;  
   char buffer[10] = {0};
   if(pipe(fd) < 0){
        perror(NULL);
        exit(1);
   }
   pid = fork();
   assert(pid >= 0);
   if (pid != 0) {  // parent
      close(fd[0]); // writer, don't need fd[0]
      write(fd[1], "123456789\n", 10);
      close(fd[1]);
      waitpid(pid, NULL, 0);
   }
   else {        
      dup2(fd[0], 0);
      close(fd[0]);
      close(fd[1]);
      char *argv_wc[] = {"/usr/bin/wc", NULL};
      execv(argv_wc[0],argv_wc);
      perror("exec");
      return 1;
   }
   return 0;
}