bash Quick 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
a The ** operator is right-associative. Prior to Version 3.1, it was left-associative.
++ - -	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.

Examples

let "count=0" "i = i + 1"			Assign i and count
let "num % 2"				Test for an even number (( percent >= 0 && ...