linux环境下，实现的shell解释器，实现功能主要有：

1. 基本界面由输入提示符开头

2. 执行可执行文件包括参数

3. 错误提示

4. 内置简单shell 命令

cd

exit

5. 单次I/O 重定向 > <

6. 单次管道 |

7. 后台运行 &

8. 顺序执行多个命令 ；-linux environment, to achieve the shell interpreter to realize functions are: 1 basic interface to the input prompt at the beginning 2. run the executable file, including parameters of 3 error 4 built-in simple shell command cd exit 5. Single I/O redirection>　< 6 single pipe | 7. running in the background &　8 in order to execute multiple commands