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。
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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。
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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。
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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 NUM14 case ${NUM} in15 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 $4}'`m" ;;18 0) exit ;;19 *) echo "This chose is not in [0~3]." 20 esac21 echo -n "Do you continue [y/n]:"22 read continue23 if [ "${contiune}" == "n" -o "${continue}" == "N" ]24 then25 exit26 fi27 done