Shell 之Bash数学运算

expr

语法格式

expr 操作符对照表

操作符	含义
num1 \| num2	num1不为空且非0 ,返回num1 ;否则返回num2
num1 & num2	num1不为空且非0，返回num1 ;否则返回0
hum1 < num2	num1小于num2 ,返回1 ;否则返回0
num1 <= num2	num1小于等于num2 ,返回1 ;否则返回0
num1 = num2	num1等于num2 ,返回1 ;否则返回0
num1 != num2	num1不等于num2 ,返回1 ;否则返回0
num1 > num2	num1大于num2 ,返回1 ;否则返回0
num1 >= num2	num1大于等于num2 ,返回1 ;否则返回0
num1 + num2	求和
num1 - num2	求差
num1 * num2	求积
num1 / num2	求商
num1 % num2	求余

=号判断使用$(($num1 = $num2))会出错，但使用==时可以
运行成功时 echo $?返回0

num1=20
num2=100
expr $num1 \| $num2
expr $num1 \& $num2
expr $numl \< $num2
expr $num1 \< $num2
expr $num1 \<= $num2
expr $num1 \> $num2
expr $num1 \>= $num2
expr $num1 = $num2
expr $num1 != $num2
expr $num1 + $num2
expr $num1 - $num2
expr $num1 \* $num2
expr $num1 / $num2
expr $num1 % $num2

求和案例

#!/bin/bash

while true
do
	read -p "Please input a postive number: " num
	# 不需要expr $num + 1的返回值
	expr $num + 1 &> /dev/null
	#判断是不是整形
	if [ $? -eq 0 ];then
		if [ `expr $num \> 0` -eq 1 ];then
			for((i=1;i<=$num;i++))
			do 
				sum=`expr $sum + $i`
			done
			echo "The ans is $sum"
			exit
		fi
	fi
	echo "illegal input"
	continue

done

bc

bc是bash内建的运算器, 支持浮点数运算

内建变量scale可以设置,默认为0

bc操作符对照表

操作符	含义
num1 + num2	求和
num1 - num2	求差
num1 * num2	求积
num1 / num2	求商
num1 % num2	求余

案例

[root@master datas]# echo "23+35" | bc
58

[root@master datas]# echo "scale=5;23/35" | bc
.65714

# Shell 之Bash数学运算

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lyhcc

DT Developer

Hunan,China

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Shell 之Bash数学运算

expr

求和案例

bc

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