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

int main(int argc, char *argv[]) {
  int p[2];
  int pid;
  int res;
  char buf[100];
  int status;

  if(argc != 2) {
    fprintf(stderr, "Usage: %s <program>\n", argv[0]);
    exit(1);
  }

 again:
  res= pipe(p);
  if(res < 0) {
    perror("pipe");
    exit(1);
  }
  pid= fork();
  if(pid == -1) {
    perror("fork");
    exit(1);
  } else if(pid == 0) {
    /* Child. */
    res= dup2(p[1], 1);
    if(res < 0) {
      perror("dup2");
      exit(1);
    }
    close(p[0]);
    close(p[1]);
    res= execl(argv[1], argv[1], 0);
    if(res < 0) {
      perror("exec");
      exit(1);
    }
  } else {
    /* Parent. */
    close(p[1]);
    do {
      res= read(p[0], buf, sizeof(buf));
    } while(res > 0);
    close(p[0]);
    res= waitpid(pid, &status, 0);
    if(res == -1) {
      perror("wait4");
      exit(1);
    }
    printf("Child=%d waitpid=%d\n", pid, res);
    goto again;
  }
}