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This article introduces the relevant knowledge of "how to realize the mathematical operation of Linux Shell script". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Arithmetic operations are essential in any programming language, and 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, it is saved as a string. We can make these variables arithmetic by using operators such as let, (), [], and so on. For example:

The code is as follows:

#! / bin/bash

No1=4 # here no1 is stored as a semantic string

No2=5 # here no2 is stored as a semantic string

Let result=no1+no2

The output of echo $result # is 9

Let no1++ # is equivalent to let no1=no1+1

The output of echo $no1 # is 5

Let no2-- # is equivalent to let no2=no2-1

The output of echo $no2 # is 4

Let no1+=5 # is equivalent to let no1=no1+5

The output of echo $no1 # is 10

Let no1-=5 # is equivalent to let no1=no1-5

The output of echo $no1 # is 5

No1=4 # here no1 is stored as a semantic string

No2=5 # here no2 is stored as a semantic string

Result=$ [no1 + no2]

The output of echo $result # is 9

Result=$ [$no1 + 5] # ubuntu does not work properly, no1 not found

The output of echo $result # is 9

Result=$ ((no1 + 50)) # the $before parentheses cannot be lost, otherwise an error will be reported.

The output of echo $result # is 54

Third, use expr for arithmetic operations

The code is as follows:

Expr is a more advanced operator than the above three operators, which can alert you to advanced operations. For example:

#! / bin/bash

Result= `expr 3 + 4` # instead of using single quotation marks, it is the symbol of the key above the tab key

The output of echo $result # is 7

Every space between result= `expr 3 + 4` # 3 and + sign

The output of echo $result # is 3x4

Note: the methods in 1.5.1 and 1.5.2 can only calculate integers, not floating-point numbers.

Third, use bc for arithmetic operations

Bc is an advanced tool for mathematical operations. This precision calculator contains a large number of options, parameters are usually placed before the specific operation to be performed, and a semicolon is used as a delimiter to pass a bc through sdtin. For example:

Echo "4 * 0.56" | the output result of bc # is 2.24

The code is as follows:

No=54

Result= `echo "$no * 1.5" | bc`

The output of echo $result # is 81.0

Echo "scale=2;3/8" # passes the precision of scale tongue decimal, and the output result is 0.37

No=100

Echo "obase=2;$no" | bc # binary conversion. Target binary is binary, default primitive is 10.

No=1100100

Echo "obase=10;ibase=2;$no" | bc # obase=10,ibase=2

Echo "sqrt (100)" | bc # calculates square root

Echo "10 ^ 10" | bc # squared

-Note: obase is the target base, ibase is the primitive, and by default the primitive is 10. 0.

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