脚本要求：
执行脚本后
接受输入1，显示当前时间，并提示是否继续选择。
接受输入2，显示CPU负载，并提示是否继续选择。
接受输入3，显示剩余内存，并提示是否继续选择。
接受输入0，退出脚本。
·····················································································································
思路:
显示当前时间
[root@wk ~]# date +%T
08:26:04
················································································································································································································
uptime命令能显示1）当前系统时间；
2）本机已经运行时间；
3）当前系统有几个用户连接；
4）本机最近1分钟、5分钟、15分钟系统的平均负载。
如下：
我们可以将uptime的输出结果用awk来进行选择输出。
····················································································································································································································
free -m 命令能以M为单位显示内存使用情况，还有交换分区swap的使用情况 ，可用awk打印出Mem行第4列的信息，即是我们要的信息。
······················································································································································································································
至于提示是否继续选择，可以用while循环。最终脚本如下：
1 #!/bin/bash
2 #
3 while [ "1" == "1" ]
4 do
5 clear
6 echo "~~~~~~~~~~~~~~~~~~~menu~~~~~~~~~~~~~~~~~~~~~~"
7 echo " 1) Time Now "
8 echo " 2) CPU Load "
9 echo " 3) Memory Free "
10 echo " 0) Exit "
11 echo "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"
12 echo "Please enter a chose[0~3]:"
13 read NUM
14 case ${NUM} in
15 1) echo "Time Now :`date +%T`" ;;
16 2) echo "CPU Load :`uptime |awk -F'[:,]' '{print $6}'`" ;;
17 3) echo "Memory Free :`free -m |awk '$1=="Mem:" {print $4}'`m" ;;
18 0) exit ;;
19 *) echo "This chose is not in [0~3]."
20 esac
21 echo -n "Do you continue [y/n]:"
22 read continue
23 if [ "${contiune}" == "n" -o "${continue}" == "N" ]
24 then
25 exit
26 fi
27 done