In this chapter, we've discussed everything parameter expansion in Bash. We started by recapping how we've used parameter substitution throughout most of this book, and how parameter substitution is only a small part of Bash parameter expansion.
We moved on to show you how we can use parameter expansion to include default values for variables, in case the user does not supply their own. This functionality also allows us to present the user with an error message if input is missing, although not in the cleanest way.
We ended this introduction to parameter expansion by showing you how we could use this to determine the length of variable values, and we showed you how we've actually used that extensively in the book already, in the form of the $# syntax.
We continued with describing parameter expansions under the heading of Variable manipulation. This...
