Arithmetic evaluation (command)
(( <EXPRESSION> ))
This command evaluates the arithmetic expression
If the expression evaluates to 0 then the exit code of the expression is set to 1 (
FALSE). If the expression evaluates to something else than 0, then the exit code of the expression is set to 0 (
TRUE). For this return code mapping, please see this section.
The functionality basically is equivalent to what the ''let'' builtin command does. The arithmetic evaluation compound command should be preferred.