Compare digital subtraction based on shell scripts no BC

The following methods can not install the BC calculator

Create sh file

Check

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v#!/bin/Bashread-P"Please enter the first number"Aread-P"Please enter a second number"Becho"and the"' Expr $a +$b ' #第一种方法echo"and the"$[$a +$b] #第二种方法echo"and the"$ (Expr $a +$b) #第三种方法echo"and the"$ (($a +$b)) #第四种方法~
They came up with the same result.

Compare digital subtraction based on shell scripts no BC