Perl Cookbook

Chapter 4. Arrays

Introduction

Works of art, in my opinion, are the only objects in the material universe to possess internal order, and that is why, though I don’t believe that only art matters, I do believe in Art for Art’s sake.

—E.M. Forster

If you are asked about the contents of your pockets, or the names of the last three presidents, or how to get to the highway, you recite a list: you name one thing after another in a particular order. Lists are part of your conception of the world. With Perl’s powerful list- and array-handling primitives, you can translate this world view directly into code.

In this chapter, we’ll use the terms list and array as the Perl language thinks of them. Take ("Reagan", "Bush", "Clinton"); that’s a list of the last three American presidents, in order. To store that list into a variable, use an array, as in @presidents = ("Reagan", "Bush", "Clinton"). Both are ordered groups of scalar values; the difference is that an array is a named variable, one whose array length can be directly changed, whereas a list is a more ephemeral notion. You might think of an array as a variable and a list as the values it contains.

This distinction may seem arbitrary, but operations that modify the length of these groupings (like push and pop) require a proper array and not merely a list. Think of the difference between $a and 4. You can say $a++ but not 4++. Likewise, you can say pop(@a) but not pop (1,2,3).

The most important thing to glean from this is that Perl’s ...