Bash arithmetic operation

I. Arithmetic Operators

**: Calculate the power of two variables.

Others: +-*/% + =-= * =/= % =

 

Ii. Operation Sequence

If the operation order is not changed without expr or $ [], the operation is assigned a value in the form of a string.

EHCO 1 + 2; the result will be 1 + 2 !!

Method 1: Use expr to represent the following expression as a mathematical operation

Note + there must be spaces before and after !! Otherwise, no arithmetic operation is performed.

 
Echo 'expr1+2`
 

Method 2: use $ [] to represent mathematical operations. Write a mathematical operation to the brackets of the $ [] symbol.

 
A = $ [$ A + 1]
 

 

3. A simple instance

Mathematical function S = 3 (x ^ y) + 4x ^ 2 + 5y + 6

Note: $1 and $2 are the values of the first and second variables respectively.

 
./Test. Sh 2 4
 

 # ! /Bin/bash
# Test. Sh  
 S = 0               #  Defines a sum variable. The initial value is 0.  
 T = 'expr $ 1 ** $ 2 ' #  Use expr to change the operation order and obtain the power y of X.  
 T = $ [T * 3 ] #  T multiplied by 3.  
 S = $ [S + T] #  Result addition.  
 T = $ [$ 1 ** 2 ] #  Returns the square of X.  
 T = $ [T * 4 ] #  The result is multiplied by 4.  
 S = $ [S + T] #  Result addition.  
 T = 'expr $ 2 * 5 ' #  Evaluate the value of 5y.  
 S = $ [S + T] #  Result addition.  
 S = $ [S + 6 ] #  6 is added to the result.  
 Echo $ S              #  Output result.