Perl reusable code is all about separation of namespace code and careful management of variable scope.

Here are some thoughts on it.

require() function is like #include in C programming, but keeps the lexical scope, meaning that any variable with `my' will not leak to the code that imports it.

It compiles at run time, (compiles just when it about to be used) which has the possibility that it will not run because errors. Perl addresses the issue by requiring that the code imported must evaluate to true, thus the return of 1; at most modules

The syntax:

Code:

require "filename"; # a string

or

Code:

require Name; # bare word, no quotes (caps in the first letter is a convention) it would look for a module Name.pm

Packages separates subroutine into namespaces. Every subroutine in Perl lives inside a package, every file begins with implicit package main;

__PACKAGE__ will tell you were you are

The syntax:

Code:

package package; # name, not quotes

or

Code:

package package {...}

In Perl, object oriented and reusable code programming is all about the scope of variables, and subroutines are variables of packages

Code:

use Foo;

is equivalent to:

Code:

BEGIN {
   require Foo; # we have explained require function before. require can have a string or bareword.
   Foo::import(); # calls the subroutine import() on the package Foo
}

use can only take a bareword, not a string.

A BEGIN code is code that runs at compile time, meaning that as soon as the compiler encounters a BEGIN block, Perl will compile it and run it before even the code that follows is compiled.