bash Pocket Reference

Arithmetic Expressions

The let command performs arithmetic. Bash is restricted to integer arithmetic. The shell provides a way to substitute arithmetic values (for use as command arguments or in variables); base conversion is also possible:

$(( expr ))	Use the value of the enclosed arithmetic expression.
B#n	Interpret integer n in numeric base B. For example, 8#100 specifies the octal equivalent of decimal 64.

Operators

The shell uses arithmetic operators from the C programming language, in decreasing order of precedence.

Operator	Description
++ --	Auto-increment and auto-decrement, both prefix and postfix
+ -	Unary plus and minus
! ~	Logical negation and binary inversion (one’s complement)
**	Exponentiation[a]
* / %	Multiplication, division, modulus (remainder)
+ -	Addition, subtraction
<< >>	Bitwise left shift, bitwise right shift
< <= > >=	Less than, less than or equal to, greater than, greater than or equal to
== !=	Equality, inequality (both evaluated left to right)
&	Bitwise AND
^	Bitwise exclusive OR
|	Bitwise OR
&&	Logical AND (short circuit)
||	Logical OR (short circuit)
?:	Inline conditional evaluation
= += -=
*= /= %=
<<= >>=	Assignment
&= ^= |=
,	Sequential expression evaluation
[a] The ** operator is right-associative. Prior to version 3.1, it was left-associative.

Examples

let "count=0" "i = i + 1"       Assign values to i and count
let "num % 2"                   Exit successfully if num is even
(( percent >= 0 && \
   percent <= 100 ))            Test the range of a value ...