Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

Perl offers several different ways to include code from one file into another. Here are the deltas between the various inclusion constructs:

    1)  do $file is like eval `cat $file`, except the former:
        1.1: searches @INC and updates %INC.
        1.2: bequeaths an *unrelated* lexical scope on the eval'ed code.

    2)  require $file is like do $file, except the former:
        2.1: checks for redundant loading, skipping already loaded files.
        2.2: raises an exception on failure to find, compile, or execute $file.

    3)  require Module is like require "Module.pm", except the former:
        3.1: translates each "::" into your system's directory separator.
        3.2: primes the parser to disambiguate class Module as an indirect object.

    4)  use Module is like require Module, except the former:
        4.1: loads the module at compile time, not run-time.
        4.2: imports symbols and semantics from that package to the current one.

In general, you usually want use and a proper Perl module.