Linux Shell Script Tutorial Series (v): Mathematical operations _linux Shell

Arithmetic operations are essential in any programming language, and the shell is no exception.

First, use Let, (()) and [] for arithmetic operations

You can use the normal variable assignment method to define a numeric value, which is that it will be saved as a string. We can use Let, (()), [] and other operators to make these variables to perform arithmetic operations. For example:

Copy Code code as follows:

#!/bin/bash
No1=4 #此处no1义字符串形式存储
No2=5 #此处no2义字符串形式存储
Let Result=no1+no2
Echo $result #输出结果为 9
Let-no1++ #等价于 let no1=no1+1
echo $no 1 #输出结果为5
Let-no2--#等价于 let no2=no2-1
Echo $no 2 #输出结果为 4
Let-no1+=5 #等价于 let no1=no1+5
echo $no 1 #输出结果为10
Let-no1-=5 #等价于 let No1=no1-5
echo $no 1 #输出结果为 5

No1=4 #此处no1义字符串形式存储
No2=5 #此处no2义字符串形式存储
result=$[No1 + NO2]
echo $result #输出结果为9
result=$[$no 1 + 5] #ubuntu中不能正常运行, No1 not found
echo $result #输出结果为9
result=$ ((no1 +)) #括号前的 $ is not to be lost, otherwise the error
echo $result #输出结果为 54

Third, using expr for arithmetic operations

Copy Code code as follows:

Expr is a more advanced operator than the above three operators, and can alert advanced operations. For example:
#!/bin/bash
result= ' Expr 3 + 4 ' #此处用的不是单引号, but the TAB key above the symbol
echo $result #输出结果为7
result= ' expr 3+4 ' #3与 + number per space
echo $result #输出结果为 3+4

Note: The methods in 1.5.1 and 1.5.2 can only be evaluated for integers and cannot be counted in floating-point numbers.
third, the use of BC for arithmetic operations

BC is an advanced tool for mathematical operations, which contains a large number of options that are usually placed before the specific operation to be performed, with semicolons as delimiters, passing a BC through Sdtin. For example:
echo "4 * 0.56" | BC #输出结果为2 24

Copy Code code as follows:

no=54
Result= ' echo ' $no * 1.5 | BC '
echo $result #输出结果为81.0

echo "Scale=2;3/8" #通过scale舌质小数的精度, the output is 0.37

no=100
echo "Obase=2 $no" | BC #进制转换, the target is binary, the default original system is 10
no=1100100
echo "Obase=10;ibase=2 $no" | BC #obase =10,ibase=2
echo "sqrt (100)" | BC #计算平方根
echo "10^10" | BC #计算平方

-Note: Obase is the target, IBase is the original, by default the original system is 10.