shell 数学计算的N个方法

let使用方法

[email?protected]:/tmp# n1=5
[email?protected]:/tmp# n2=10
[email?protected]:/tmp# let result=n1+n2
[email?protected]:/tmp# echo $result
15
[email?protected]:/tmp# let n1++
[email?protected]:/tmp# echo $n1
6
[email?protected]:/tmp# let n1--
[email?protected]:/tmp# echo $n1
5
[email?protected]:/tmp# let n1+=6
[email?protected]:/tmp# echo $n1
11

$[] 来计算

[email?protected]:/tmp/pratice# n1=5
[email?protected]:/tmp/pratice# n2=10
[email?protected]:/tmp/pratice# result2=$[ n1 + n2 ]
[email?protected]:/tmp/pratice# echo $result2
15

$(()) 计算

[email?protected]:/tmp# echo $(( 1+2 ))
3
[email?protected]:/tmp# echo $((1-9))
-8

expr 来计算

[email?protected]:/tmp# result=`expr 10-3`  # 运算符前后没有空格间隔，导致无法运算
[email?protected]:/tmp# echo $result
10-3
[email?protected]:/tmp# result=`expr 10 - 3`
[email?protected]:/tmp# echo $result
7
[email?protected]:/tmp# result=$(expr $n1 + 4)
[email?protected]:/tmp# echo $result
15
[email?protected]:/tmp# echo $n1
11

bc 来计算

[email?protected]:/tmp# echo "4*12*0.3" | bc
14.4
[email?protected]:/tmp# result2=`echo "4*12*0.3" | bc`
[email?protected]:/tmp# echo $result2
14.4

通过scale来控制精度

[email?protected]:/tmp# echo "scale=3;3.1415926*7/2.1234987" | bc
10.356
[email?protected]:/tmp# echo "scale=30;3.1415926*7/2.1234987" | bc
10.356092141709340344780997511324

10进制与2进制转换

[email?protected]:/tmp# n=100
[email?protected]:/tmp# echo "obase=2;$n" | bc
1100100
[email?protected]:/tmp# n2=1100100
[email?protected]:/tmp# echo "obase=10;ibase=2;$n2" | bc
100