Bash Quick Start Guide

Doing math in Bash

Bash supports simple integer (whole number) arithmetic operations with its arithmetic expressions. The syntax for expanding these is a set of double parentheses after the usual $ expansion sign:

$ num_a=3
$ num_b=2
$ printf 'The sum of the two numbers is: %u\n' "$((num_a + num_b))"
The sum of the two numbers is: 5

Notice in the preceding expression, "$((num_a + num_b))", we did not have to use the $ prefix to expand the num_a and num_b variables names. Assignments to other variables can be performed in the same way:

$ diff="$((num_a - num_b))"
$ printf 'The difference of the two numbers is: %u\n' "$diff"
The difference of the two numbers is: 1

We can do many different kinds of operations with these expressions, using both ...