7 – Seeing The World As The Shell Sees It

Arithmetic Expansion

The shell allows arithmetic to be performed by expansion. This allow us to use the shell

prompt as a calculator:

[me@linuxbox ~]$ echo $((2 + 2))

Arithmetic expansion uses the form:

$((expression))

where expression is an arithmetic expression consisting of values and arithmetic opera-

tors.

Arithmetic expansion only supports integers (whole numbers, no decimals), but can per-

form quite a number of different operations. Here are a few of the supported operators:

Table 7-1: Arithmetic Operators

Operator Description

Addition

Subtraction

Multiplication

Division (but remember, since expansion only supports integer

arithmetic, results are integers.)

Modulo, which simply means, “ remainder.”

Exponentiation

Spaces are not significant in arithmetic expressions and expressions may be nested. For

example, to multiply 5 squared by 3:

[me@linuxbox ~]$ echo $(($((5**2)) * 3))

Single parentheses may be used to group multiple subexpressions. With this technique,

we can rewrite the example above and get the same result using a single expansion in-

stead of two: