String and Arithmetic Expansion

Part of the Bash course

You will constantly find yourself with a variable that holds almost, but not quite, what you need. A full file path when you only want the filename. A filename when you only want the extension. A sentence where one word needs swapping out. A pair of numbers you need added together for a report.

Imagine a price tag that reads $19.99 and you want just the number, 19.99, with the dollar sign trimmed off the front. Or a photo file called vacation.jpg where you want just vacation, with the .jpg trimmed off the back. Bash has a piece of syntax for exactly this kind of trimming, and it does not need any external tool. ...