掌握系统调用pipe()的使用方法及其功能，理解管道通信原理； （２）掌握利用系统调用exit()和wait()实现父进程与子进程之间的同步，理解同步的含义。 -Master the system call pipe () to use its functions, to understand the pipeline communication theory (2) master system call exit () and wait () synchronization betw