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arithmetic substitution

summary

    This subchapter looks at arithmetic substitutions in UNIX (and Linux).

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arithmetic substitution

    This subchapter looks at arithmetic substitutions in UNIX (and Linux).

arithmetic substitution

    You can use arithmetic substitution for quick integer artihmetic.

    Place an integer arithmetic expression inside double parenthesis and place a dollar mark before the parenthesized expression (wow, that’s a lot of words), $(( expression )).

    $(( 5 + 3 ))

    You may use integer constants or integer variables:

    $(( 5 + $z ))

    You may post-increment, post-decrement, pre-increment, or pre-decrement variables:

    $(( --x + z++ ))

    You may use negative integers:

    $(( -1 * -2 ))

    You may use logical (!) and bitwise (~) negation:

    $(( !1 * ~2 ))

    The order of precedence (and complete list of possible operations):

operator	meaning
VAR++ VAR--	variable post-increment and pre-increment
++VAR --VAR	variable pre-increment and pre-decrement
- +	unary minus and plus
! ~	logical negation and bitwise negation
**	exponentiation
* / %	multiplication, division, and modulo
+ -	addition and subtraction
<< >>	left bitwise shift and right bitwise shift
<= >= < >	comparison operators
== !=	equality and inequality
&	bitwise AND
^	bitwise exclusive OR
|	bitwise OR
&&	logical AND
||	logical OR
expression ? expression : expression	C-style conditional evaluation
= *= /= %= += -= <<= >>= &= ^= !=	assignments
,	separator between expressions

    Applying the precedence rules:

    $(( ((3 + 5*2) -8) /2 ))

    The result for the above expression is 2. It is not 2.5 because this is integer arithmetic. It is not 4 because the multiplcation has a higher precedence than addition.

    You can have a raw expression, which is useful if it includes an assignment operator:

    $ n=1
    $ echo $n
    1
    $ (( n += 3 ))
    $ echo $n
    4
    $

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