/* fork.c - demo of fork and exec 
 */

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

main(int argc, char **argv)
{
  char *newargv[3];
  int i, j;
  extern int errno;

  newargv[0] = "cat";
  newargv[1] = "f1";
  newargv[2] = NULL;

  for (j = 1; j <= 4; ++j)
  {
    /* Print out Process ID.  Used to prove we are running this loop
     * in our child process.  ... Force output
     */
    printf("I am %d.  j = %d\n", getpid(), j);
    fflush(stdout);

    /* 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 ("    process %d has just been born\n", getpid());
      i = execv("/usr/bin/cat", newargv);      
      printf ("    pid = %d:  execv returned %d  ", getpid(), i);
      if (i == -1)
        printf ("    errno = %d", errno);
      printf ("\n");
    }
    else
    {
      /* The parent:  if we successfully called cat, we are going to "wait"
       * until it finishes and then only move on from there.
       */
      printf ("  pid = %d:  i = %d...", getpid(), i);
      printf ("wait returns %d...", wait(&i));
      printf ("i = %d\n", getpid(), i);
    }
  }
}
/*------------------------ Example output ------------------------------
I am 24004.  j = 1
     process 24005 has just been born
     this is the file f1
pid = 24004:  i = 0...wait returns 24005...i = 24004
I am 24004.  j = 2
    process 24006 has just been born
    this is the file f1
pid = 24004:  i = 0...wait returns 24006...i = 24004
I am 24004.  j = 3
    process 24007 has just been born
    this is the file f1
pid = 24004:  i = 0...wait returns 24007...i = 24004
I am 24004.  j = 4
    process 24008 has just been born
    this is the file f1
pid = 24004:  i = 0...wait returns 24008...i = 24004
------------------------------------------------------------------------*/