Linux Shell Script Raiders (1.5)

1.5 using the shell for mathematical operations

In any programming language, arithmetic operations are essential, and the shell is no exception.

1.5.1 arithmetic operations using Let, (()), and []

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

#!/bin/bashno1=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 LetResult=no1+no2Echo $result                 #输出结果为 9 Letno1++#等价于 let No1=no1+1Echo $no 1                    #输出结果为5 Letno2--#等价于 let no2=no2-1Echo $no 2                    #输出结果为 4 Letno1+=5                   #等价于 let No1=no1+5Echo $no 1                    #输出结果为10 Letno1-=5                   #等价于 let No1=no1-5Echo $no 1                    #输出结果为 5no1=4                        #此处no1义字符串形式存储No2=5                        #此处no2义字符串形式存储result=$[No1 + NO2]Echo $result                 #输出结果为9result=$[$no 1+5]#ubuntu中不能正常运行, No1 not foundEcho $result                 #输出结果为9result=$ ((No1 + -))#括号前的 $ must not be lost, otherwise errorEcho $result                 #输出结果为

1.5.2 using expr for arithmetic operations

• Expr is a more advanced operator than the above three operators and can alert you to advanced actions. For example:

#!/bin/bash34`     #此处用的不是单引号，而是tab键上面那个键的符号echo$result            #输出结果为7      3+4`       #3与+号之间每空格echo$result            #输出结果为 3+4                          

• Note: Methods in both 1.5.1 and 1.5.2 can only be evaluated on integers and cannot be calculated with floating-point numbers.

1.5.3 using BC for arithmetic operations

• BC is a high-level tool for mathematical operations, this precision calculator contains a number of options, the parameters are usually placed before the specific operation to be performed, and a semicolon as a delimiter, passed through Sdtin BC. For example:

Echo "4 * 0.56"| Bc#输出结果为2.no= WuResult= 'Echo "$no * 1.5"| BC 'Echo $result#输出结果为81.0Echo "SCALE=2;3/8"#通过scale舌质小数的精度, the output is 0.37no= -Echo "obase=2; $no"| Bc#进制转换, the target binary is binary, and the default original system is tenno=1100100Echo "obase=10;ibase=2; $no"| Bc#obase =10,ibase=2Echo "sqrt (+)"| Bc#计算平方根Echo "10^10"| Bc#计算平方

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

1.5.4 Reference

Linux Shell Script Raiders

Linux Shell Script Raiders (1.5)