用C语言编写一个简单的shell程序，清晰易读、设计优良.使用Linux下的软件开发工具,学习使用POSIX/UNIX系统调用、对进程进行管理和完成进程之间的通信,理解并发程序中的同步问题.-A simple shell program written in C language, legible, well-designed software development tools under Linux, learning to use the POSIX/UNIX system call, the process of communication between the management and completion of the process, understanding the concurrent program synchronization problems.