Using the let command for arithmetic

We can use the bash built-in command let for performing arithmetic operations.
To get more information about let, type the following:

    $ help let
  

This should produce the following output of this command:

Let's start using the let command:

    $ value=6
    $ let value=value+1
    $ echo $value
    7
    $ let "value=value+4"
    $ echo $value
    11
    $ let "value+=1"
    #above expression evaluates as value=value+1
    $ echo $value
    12  

A summary of operators available with the let command follows:

• Operation: Operator
• Unary minus: -
• Unary plus: +
• Logical NOT: !
• Bitwise NOT (negation): ~
• Multiply: *
• Divide: /
• Remainder: %
• Subtract: -
• Add: +

Prior to Bash 2.x, the following operators were not available:

• Bitwise left shift: <<
• Bitwise right shift: >>
• Equal to and not equal to: ==, !=
• Comparison...