Linux in a Nutshell, Fourth Edition

Arithmetic Expressions

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

Expression	Meaning
(( expr ))	Use the value of the enclosed arithmetic expression.

Operators

bash uses arithmetic operators from the C programming language; the following list is in decreasing order of precedence. Use parentheses to override precedence.

Operator	Meaning
-	Unary minus
! ~	Logical negation; binary inversion (one’s complement)
* / %	Multiplication; division; modulus (remainder)
+ -	Addition; subtraction
<< >>	Bitwise left shift; bitwise right shift
<= >=	Less than or equal to; greater than or equal to
< >	Less than; greater than
= = !=	Equality; inequality (both evaluated left to right)
&	Bitwise AND
^	Bitwise exclusive OR
|	Bitwise OR
&&	Logical AND
||	Logical OR
=	Assign value
+= -=	Reassign after addition/subtraction
*= /= %=	Reassign after multiplication/division/remainder
&= ^= |=	Reassign after bitwise AND/XOR/OR
<<= >>=	Reassign after bitwise shift left/right

Examples

See the let built-in command for more information and examples.

               let "count=0" "i = i + 1"      
               Assign i and count
               let "num % 2"; echo $?               
               Test for an even number