// file: test.c
// Comp.Sys.Org.II, Spring 2005, Yap.
// The following code is a simple modification of the "fork.c" code from
//
// Dr Ian G Graham, Department of Information Technology, GUGC
// Copyright © 2000-2003
//
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/wait.h>
 
extern int errno;     /* system error number */
 
void syserr(char* );  /* error report, abort routine */ 
 
int main(int argc, char *argv[])
{
   pid_t pid;
   int rc;
 
   pid = getpid();
   printf("Process ID before fork: %d\n", pid);
	
   switch (fork()) {
      case -1:
         syserr("fork");
      case 0:
      
/* execution in child process */ 
 
         pid = getpid();
         printf("Process ID in child after fork: %d\n", pid);
         execlp("echo", "0", "Child to world: Hello!",NULL);
         syserr("execl");
   }
 
/* continued execution in parent process */
 
   pid = getpid();
   printf("Process ID in parent after fork: %d\n", pid);
 
   //getchar(); // supposed to hang until I type something
   exit(0);
}
 
void syserr(char * msg)
{
   fprintf(stderr,"%s: %s", strerror(errno), msg);
   //abort(errno); // variant
   abort();
}