Programming Perl, 3rd Edition

Chapter 30. The Standard Perl Library

The standard Perl distribution contains much more than just the perl executable that executes your scripts. It also includes hundreds of modules filled with reusable code. Because the standard modules are available everywhere, if you use one of them in your program, you can run your program anywhere Perl is installed, without any extra installation steps.

Library Science

Before we enumerate these modules in the following chapters, let's review a bit of the terminology we've been splattering about.

namespace

A namespace is a place to keep names so they won't be confused with names in other namespaces. This leaves you with the simpler problem of not confusing the namespaces themselves. There are two ways to avoid confusing namespaces with each other: give them unique names, or give them unique locations. Perl lets you do both: named namespaces are called packages and unnamed namespaces are called lexical scopes. Since lexical scopes can be no larger than a file, and since the standard modules are file-sized (at minimum), it follows that all module interfaces must make use of named namespaces (packages) if they're to be used by anyone outside the file.

package

A package is Perl's standard mechanism for declaring a named namespace. It's a simple mechanism for grouping together related functions and variables. Just as two directories can both contain a (different) file named fred, two different parts of a Perl program can each have its own $fred variable ...