/* fork1.c - demo of fork and exec
 * Note that exec takes 2 parameters:  name of binary; argument list
 */
#include <stdio.h>
#include <unistd.h>

main(int argc, char **argv)
{
  char *catarg[3];
  int i, j, return_value;

  /* Here are the arguments to pass to child process "cat f1.txt".
  */
  catarg[0] = "cat";
  catarg[1] = "f1.txt";
  catarg[2] = NULL;

  for (j = 1; j <= 4; ++j)
  {
    /* Print out Process ID.  Used to prove which process is talking.
     */
    printf("I am process %d.  Iteration %d\n", getpid(), j);


    /* Try to fork and create a new process address space, then
     * in the child:  attempt to exec the 'cat' program/command.
     */
    if (fork() == 0)
    {
      printf ("      Child process %d has just been born\n", getpid());

      i = execv("/bin/cat", catarg);
      printf ("      (child) pid = %d:  execv returned %d\n", getpid(), i);
    }
    else
    {
      /* The parent:  if we successfully called cat, we are going to "wait"
       * until it finishes and then only move on from there.
       */
      printf ("   (parent) pid = %d:  i = %d    ", getpid(), i);
      return_value = wait(&i);
      printf ("wait returns %d    ", return_value);
      printf ("wait changed i to %d\n\n", i);

    }
  }
}