linux下的命令解释器，能执行部分内部和外部命令，支持I/O重定向，管道和前后台作业及控制，能够执行fg、bg、jobs、cd、history、exit这些内部命令,能够执行带参数的外部命令,支持I/O重定向,支持前后台作业

。-linux command interpreter, part of the internal and external commands, support for I/O redirection, pipes, and front and back office operations and control, and be able to perform fg, bg, jobs, cd, history, and exit these internal commands, able to perform with The parameters of the external command to support I/O redirection and support before and after the operation.