Learn Linux Shell Scripting - Fundamentals of Bash 4.4

Parameter expansion

In this second-to-last chapter, with the final chapter being tips and tricks, we will deal with a very cool feature of Bash: parameter expansion.

We'll begin with a few notes on terminology. First of all, what's considered parameter expansion in Bash deals with more than just parameters/arguments supplied to a script: all special operations we'll be discussing in this chapter are applicable to Bash variables. In the official Bash manual page (man bash), these are all referred to as parameters.

For positional arguments to scripts, or even options with arguments, this makes sense. However, once we enter the territory of constants defined by the script creator, the distinction between a constant/variable and a parameter gets ...