shell中计算除法，基本的方法有几种
t1=3
t2=6
1）expr
num=`expr $(($t1/$t2))`
num的结果为0，因为expr不支持浮点算法
2）bc
echo "scale=2;$t1/$t2"|bc
scale用来控制小数点后面保留的位数
3）awk
awk 'BEGIN{printf "%.2f%\n",('$t1'/'$t2')}'
awk 'BEGIN{printf "%.2f%\n",('$t1'/'$t2')*100}'
 
乘法
usage_mem_percent=`echo $t1 \* 100|bc`
 
加法：
total_cpu_percent=`echo "$t1 $t2"|bc`
 
比较：
flag=`expr $usage_cpu \> "0.95"` 大于 flag=1
 
例子（监控cpu和内存总占用量大于95%报警发邮件）：
 

1.#!/bin/sh

2.MAILX=/usr/bin/mailx

3.NOTIFY="194915592@qq.com"

4.FROM="***@****.com"

5.DATE=`date %Y%m%d%H`

6.DIR="/root/monitor/"

7.HOSTNAME=`hostname`

8.NUM="100"

10.cd $DIR

11.rm report_cpu_mem.`date -d -1day %Y%m%d`*

12.rm report_cpu_mem.$DATE

13.########################### cpu ##########################

14.#system used percent of cpu and user used percent of cpu e.g 3.2%usr , 4.5%sys , user_cpu_percent=3.2 ,sys_cpu_percent=4.5

15.user_cpu_percent=`top -n 1 |grep Cpu|awk '{print $2}'|cut -d "%" -f 1`

16.sys_cpu_percent=`top -n 1 |grep Cpu |awk '{print $3 }' |cut -d "%" -f 1`

18.total_cpu_percent=`echo "$user_cpu_percent $sys_cpu_percent"|bc`

19.#cpu number e.g 60% used , then usage_cpu=0.6

20.usage_cpu=`echo "scale=2;$total_cpu_percent/$NUM"|bc`

22.########################### mem ##########################

24.#total memory and used memory , e.g total 25620K , used 2222K, then total_mem=25620, used_mem=2222k

25.total_mem=`top -n 1 |grep Mem |awk '{print $3}'|cut -d "k" -f 1`

26.used_mem=`top -n 1 |grep Mem |awk '{print $5}'|cut -d "k" -f 1`

28.#memory number e.g 30% used, then usage_mem=0.3

29.usage_mem=`echo "scale=2;$used_mem/$total_mem"|bc`

31.#the percent of memory used , e.g 63.3% , then usage_mem_percent=63.6

32.usage_mem_percent=`echo "0"$usage_mem \* 100|bc`

36.flag=`expr "0"$usage_cpu \> "0.95"`

37.flag1=`expr "0"$usage_mem \> "0.95"`

39.if [ "$flag" == "1" ];then

40.echo "The cpu Utilization on $HOSTNAME is over 95%. " >>report_cpu_mem.$DATE

41.echo "user had used "$total_cpu_percent"% cpu" >>report_cpu_mem.$DATE

42.echo "system had used "$sys_cpu"% cpu">>report_cpu_mem.$DATE

43.echo "Please check below processes:" >>report_cpu_mem.$DATE

45.ps aux|head -1;ps aux|grep -v PID|sort -rn -k 3|head >>report_cpu_mem.$DATE

46.$MAILX -s "the cpu of $hostname used too much , please check it" $NOTIFY<report_cpu_mem.$DATE

47.fi

48.if [ "$flag1" == "1" ] ;then

50.echo "The mem Utilization on $HOSTNAME is over 95%. " >>report_cpu_mem.$DATE

51.echo "this host had used $usage_mem_percent"%" memory" >>report_cpu_mem.$DATE

52.echo "Please check below processes:" >>report_cpu_mem.$DATE

54.ps aux|head -1;ps aux|grep -v PID|sort -rn -k 4|head >>report_cpu_mem.$DATE

55.$MAILX -s "the host $HOSTNAME used too much memory or cpu , please check it" $NOTIFY<report_cpu_mem.$DATE

57.fi