本实验要实现一个简单的命令解释器，也就是Linux中的shell程序。实验程序起名为ysh，要求其设计类似于目前流行的shell解释程序，如bash、csh、tcsh，但不需要具备那么复杂的功能。ysh程序应当具有如下一些重要的特征：
 　　能够执行外部程序命令，命令可以带参数。　　．　。
 　　能够执行fg、bg、cd、history、exit等内部命令。
 　　使用管道和输入输出重定向。
 　　支持前后台作业，提供作业控制功能，包括打印作业的清单，改变当前运行作业的前台/后台状态，以及控制作业的挂起、中止和继续运行。
　　除此之外，在这个实验中还须做到：
 　　使用make工具建立工程。
 　　使用调试器gdb来调试程序。
 　　提供清晰、详细的设计文档和解决方案。
,This experiment in order to achieve a simple command interpreter, that is, the shell process in Linux. Experimental procedure named ysh, required that their design is similar to the current popular interpretation of the procedures of the shell, such as bash, csh, tcsh, but it does not need a less complex function. ysh procedures should have the following important features:
　external procedures to perform the command, the command can take parameters. . .
　to perform fg, bg, cd, history, exit the internal order.
　the use of input and output pipes and redirection.
　support before and after the Taiwan operations, the provision of operating control functions, including a list of print jobs, change the current operation of the front running/background status of the pending operation and control, suspension and continue to run.
　　 In addition, this experiment must be done:
　make tools to use to establish the project.
　use gdb