Knowing references (see Chapter 2) allows you to perform some advanced coding in Perl, including making hashes of hashes (a.k.a. multi-dimensional hashes). This chapter introduces this topic as well as some other advanced features of hashes.
What you should already know about hashes
Note
In the Beginning Perl Programming and Pro Perl Programming books, we covered some of the basics of hashes. This section is meant to be a review of these topics.
Hashes are useful when you need to store data that is related to (or associated with) other data, ...
