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

int main()
{
   int   fd[2];
   pid_t pid;
   int   n;
   char  line[256];
   char  *str = "hello world!\n";

   if ( pipe(fd) < 0 ) {
      fprintf(stderr, "pipe error");
      exit(-1);
   }

   if ( (pid = fork()) < 0 ) {
      fprintf(stderr, "fork error");
      exit(-1);
   } else if ( pid > 0 ) { // parent
      close(fd[0]);
      write(fd[1], str, strlen(str));
   } else { // child
      close(fd[1]);
      n = read(fd[0], line, sizeof(line));
      write(STDOUT_FILENO, line, n);
   }

   exit(0);
}