设计如下一个菜单驱动程序
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 (要求显示为：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
Q:To quit this program
Enter your option and hit:
菜单程序将根据用户输入的选择项给出相应信息。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。
#!/bin/bash function welcome()
{
echo -e "\n"
echo "Use one of the following options:"
echo "P: To display current derectory "
echo "S: To display the name of running file"
echo "D: To display today's date and present time"
echo "L: To see the listing of files in your present working directory"
echo "W: To see who is logged in"
echo "Q: To quit this program"
echo -n "Enter your option and hit:"
read a
echo -e "\n"
}
welcome
until [ $a = q -o $a = Q ];
do
case "$a" in
p|P)
pwd
welcome
;;
s|S)
echo "The running file is $0"
welcome
;;
d|D)
date
welcome
;;
l|L)
ls -a
welcome
;;
w|W)
who
welcome
;;
*)
echo -n "Sorry,your option is wrong,please enter your option again"
echo -e "\n"
read a
esac
done
echo "Thank you for your playing"
exit