expr

expr is another command that is used to evaluate arithmetic expressions similar as ‘let’ command.
But expr can’t define variables.
expr command is working as following example.

num1=1
num2=2
expr $num1 + $num2

Important :
In expr command multiplication works different way. That means this is not working.
2 * 3

Have to type '\*' to get the multiplication
2 \* 3