<p>My question is similar to "<a href="https://stackoverflow.com/questions/156362/what-is-the-difference-between-include-and-extend-in-ruby">What is the difference between include and extend in Ruby?</a>".</p>

<p>What's the difference between <code>require</code> and <code>include</code> in Ruby?  If I just want to use the methods from a module in my class, should I <code>require</code> it or <code>include</code> it?</p>

What's the difference between
  "include" and "require" in Ruby?
Answer:
The include and require methods do
  very different things.
The require method does what include
  does in most other programming
  languages: run another file. It also
  tracks what you've required in the
  past and won't require the same file
  twice. To run another file without
  this added functionality, you can use
  the load method.
The include method takes all the
  methods from another module and
  includes them into the current module.
  This is a language-level thing as
  opposed to a file-level thing as with
  require. The include method is the
  primary way to "extend" classes with
  other modules (usually referred to as
  mix-ins). For example, if your class
  defines the method "each", you can
  include the mixin module Enumerable
  and it can act as a collection. This
  can be confusing as the include verb
  is used very differently in other
  languages.
Source
So if you just want to use a module, rather than extend it or do a mix-in, then you'll want to use
```
require
```
.
Oddly enough, Ruby's
```
require
```
is analogous to C's
```
include
```
, while Ruby's
```
include
```
is almost nothing like C's
```
include
```
.