Parameter expansion in Bash deals with more than just default values, input checking, and parameter length. It actually also allows us to manipulate the variables before we use them. In this second part of this chapter, we'll explore the capabilities within parameter expansion that deal with variable manipulation (our terminology; as far as Bash is concerned, these are just normal parameter expansions).
We'll kick this off with pattern substitution, something you should be familiar with after our explanation of sed in Chapter 10, Regular Expressions.
