require vs include in Ruby

1. Use the require Method in Ruby
2. Use the include Method in Ruby

This article will clarify the differences between require and include in Ruby.

To achieve reusability and make maintenance more accessible, we must divide our features into files and modules.

Programmers can define as many modules as they want within each file.

Use the require Method in Ruby

The file name is passed as a string to the require method. It can be a path to a file, such as ./my dir/file a.rb or a simple filename without an extension, such as file a.rb.

When you use require, the code in a file is evaluated and executed.

The example shows how to use require. The message in file a.rb will be printed by the file code in file a.rb.

We’ll load file_a by calling require 'file_a' inside file file b.rb. Result in a string in file_a.rb will be printed.

# file_a.rb
puts 'in file_a.rb'

# file_b.rb
require 'file_a'

Output:

in file_a.rb

Use the include Method in Ruby

Unlike require, which loads an entire file’s code, include takes a module name and makes all its methods available to other classes or modules.

Below is the syntax for the include statement in Ruby. When we call the instance method greet from a class called HelloWorld, we get a missing error.

class HelloWorld; end
HelloWorld.new.greet

Output:

NoMethodError: undefined method `greet' for #<HelloWorld:0x007faa8405d5a8>

Then we make a Greeting module and include it in the class we created earlier. Calling greet after that will print a message.

module Greeting
  def greet
    puts 'How are you doing?'
  end
end

HelloWorld.include(Greeting)
HelloWorld.new.greet

Output:

How are you doing?