#include <sys/types.h>
#include <sys/wait.h>
#include <sys/resource.h>
#include <stdio.h>
#include <unistd.h>
#include <stdarg.h>
#include <unistd.h>
#include <stdlib.h>

void waitchildren(int signum);
void h_exit(int status);

int main(void)
{
    	pid_t pid;
    	int status;

    	if((pid=fork())<0)
    	{
        	printf("fork error!\n");
        	exit(0);
    	}
    	else if(pid==0)
    	{
        	printf("Hello from the child process%4d!\n", getpid());
        	setenv("PS1", "CHILD \ \ $", 1);
        	printf("Process%4d: I’m calling exec. \n", getpid());
		execl("/bin/sh", "/bin/sh", NULL);
		printf("Process%4d: You should never see this because the child is already gone.\n", getpid());
    	}
    	else if(pid!=-1)
    	{
        	printf("Hello from the parent process%4d!\n", getpid());
        	printf("Process%4d: The parent has forked process %d. \n", getpid(),pid);
		printf("Process%4d: The parent is waiting for the child to exit.\n", getpid());
		wait4(pid, &status, 0, NULL);
		h_exit(status);
    	}

	return 0;
}


void h_exit(int status)
{
    	if(WIFEXITED(status))
        	printf("normal termination, exit status=%d .\n", WEXITSTATUS(status));
    	else if(WIFSIGNALED(status))
        	printf("abnormal termination, exit status=%d. \n", WTERMSIG(status));
 }