#include <unistd.h>
#include <stdio.h>
#include <iostream>
#include <fcntl.h>
#include <sys/wait.h>
#include <sys/stat.h>
using namespace std;

int main(){
  pid_t returnedValue = fork();
  if(returnedValue < 0){
    perror("error forking");
    return -1;
  } else if (returnedValue == 0){
    if(close(STDOUT_FILENO) < 0){
      perror("error closing standard output");
      return -1;
    }
    // When there is no error, open returns the smallest file
    // descriptor not already in use by this process, so having
    // closed STDOUT_FILENO, the open should reuse that number.
    if(open("my-processes", O_WRONLY | O_CREAT | O_TRUNC,
            S_IRUSR | S_IWUSR) < 0){
      perror("error opening my-processes");
      return -1;
    }
    execlp("ps", "ps", "l", NULL);  // ps with option letter l
    perror("error executing ps");
    return -1;
  } else {
    if(waitpid(returnedValue, 0, 0) < 0){
      perror("error waiting for child");
      return -1;
    }
    cout << "Note the parent still has the old standard output."
         << endl;
  }
}