1. 设计如下⼀个菜单驱动程序，保存为： menu.sh 菜单程序将根据⽤户输⼊的选择项给出相应信息,直到输⼊Q|q才退出程序(循环)，否则⼀ 直提示操作信息 Use one of the following options: P:To display current directory S:To display the name of running file D:To display today's date and present time(如：2017-04-26 05:45:12) L:To see the list of files in your present working directory W:To see who is logged in I:To see the ip address of this local machine Q:To quit this program Enter your option and hit: 要求对⽤户的输⼊忽略⼤⼩写，对于⽆效选项的输⼊给出相应提示。 要求使⽤case语句实现以上功能，输⼊相应的字⺟后应该执⾏相应的命令完成每项功能，如输⼊P或 p，就执⾏pwd命令。

下面是实现菜单驱动程序的 shell 脚本 menu.sh，你可以参考一下：

#!/bin/bash

while true; do
    echo "Use one of the following options:"
    echo "P:To display current directory"
    echo "S:To display the name of running file"
    echo "D:To display today's date and present time(如：2017-04-26 05:45:12)"
    echo "L:To see the list of files in your present working directory"
    echo "W:To see who is logged in"
    echo "I:To see the ip address of this local machine"
    echo "Q:To quit this program"
    read -p "Enter your option and hit: " option
    case $option in
        [Pp])
            pwd
            ;;
        [Ss])
            echo $0
            ;;
        [Dd])
            date '+%Y-%m-%d %H:%M:%S'
            ;;
        [Ll])
            ls
            ;;
        [Ww])
            who
            ;;
        [Ii])
            hostname -I
            ;;
        [Qq])
            exit 0
            ;;
        *)
            echo "Invalid option: $option"
            ;;
    esac
done

在命令行中执行 `./menu.sh` 即可运行该程序，注意要先给该脚本添加可执行权限。