However, if forkfile has no rule number rule_num, the function should return-1 without doing anything else. If the command didn't exit normally when do_action() tried to perform it, - I should be returned. In order to perform the command of a rule, the function will have to create a child process that will run it. As above, the function should return the child process' exit status if child process exited normally- this is needed by our make_target mentioned earlier, which calls this function.