arithmetic substitution

summary

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

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):

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
$