shell中数字计算方法（bc/expr/$(())/let/awk）

Posted 2020-09-30

1.bc

常用计算工具，而且支持浮点运算：

[[email protected] shell]# echo 1+1 | bc

2

浮点数精度问题未解决

[[email protected] shell]# echo "1.2*1.2" | bc

1.4

[[email protected] shell]# echo "scale=2;1.2*1.2" | bc

1.44

[[email protected] shell]# echo "5.0/3.0" | bc

1

[[email protected] shell]# echo "scale=2;5.0/6.0"|bc

.83

 

2.expr

 不支持浮点运算，注意运算符左右都有空格，使用乘号时，必须用反斜线屏蔽其特定含义

[[email protected] shell]# expr 10 + 10

20
[[email protected] shell]# expr 1500 + 900

2400
[[email protected] shell]# expr 30 / 3

10
[[email protected] shell]# expr 30 / 3 / 2

5

[[email protected] shell]# expr 30 \* 3

90

 

3.$(())

 

同expr，不支持浮点数运算

[[email protected] shell]# echo $((1+1))

2

[[email protected] shell]# echo $((2*3))

6

[[email protected] shell]# echo $((6/2))

3

[[email protected] shell]# echo $((6/5))

1

 

4.let

不支持浮点数运算，而且不支持直接输出，只能赋值

[[email protected] shell]# let a=10+10

[[email protected] shell]# echo $a

20

[[email protected] shell]# let b=50/5

[[email protected] shell]# echo $b

10

[[email protected] shell]# let c=6*5

[[email protected] shell]# echo  $c

30

[[email protected] shell]# let c=6/5

[[email protected] shell]# echo  $c

1

 

5.awk

 

普通的运算：

[[email protected] shell]# echo|awk ‘{print(1+1)}‘

2

[[email protected] shell]# echo|awk ‘{print(1/2)}‘

0.5

[[email protected] shell]# echo|awk ‘{print(1/3)}‘

0.333333

[[email protected] shell]# echo|awk ‘{print(3*5)}‘

15

 

控制精度(printf)：

 

[[email protected] shell]# echo | awk ‘{printf("%.2f \n",1/2)}‘

0.50

[[email protected] shell]# echo | awk ‘{printf("%.4f \n",1/3)}‘

0.3333

 

传递参数：

[[email protected] shell]# echo | awk -v a=5 -v b=6 ‘{printf("%.4f \n",a/b)}‘注：该方法a，b不需加$符

0.8333

 

[[email protected] shell]# a=5

[[email protected] shell]# b=6

[[email protected] shell]# echo|awk "{print($a/$b)}"注：该方法需在大括号外打双引号

0.833333

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