HowtoMatrix

As I was writing the Time and date in Unix scripts post last week, I’ve realized that there’s one really useful feature of Unix shell scripting which I haven’t covered on my pages here: it’s the double bracket parenthesis which allows you to evaluate arithmetic expressions.

Basic arithmetic calculations in Unix scripts

In most scenarios, your script will need only basic arithmetic operations: summing or subtracting numbers, multiplying or dividing them. Using only these operations, you’ll be able to implement all sorts of counters and calculate percentages or any other progress indicators you may need.

Read more at UNIX Tutorial