Ruby Require Method

last modified October 18, 2026

This tutorial explains how to use Ruby's require method to load external code. The method is essential for modular programming in Ruby.

The require method loads a Ruby file or extension once per process. It searches the directories in $LOAD_PATH and returns true when it loads a file, or false when the feature was already loaded. A missing file raises LoadError.

require caches loaded features in $LOADED_FEATURES, so a second call returns false without executing the file again. In contrast, load executes the file every time and needs an explicit extension. require_relative resolves the path relative to the current file instead of searching $LOAD_PATH. Both require and require_relative can load native extensions as well as Ruby files.

Basic Require Example

This simple example demonstrates loading a standard library module with require. The date module provides date manipulation capabilities.

basic_require.rb

require 'date'

today = Date.today
puts "Today is #{today}"

The require 'date' loads Ruby's date module. After requiring, we can use the Date class directly. The method searches standard library paths automatically.

Requiring Local Files

This example shows how to require a local Ruby file in the same directory. require_relative resolves the path from the file containing the call, so no load path changes are needed.

mylib.rb

module MyLib
  def self.hello(name)
    "Hello, #{name}!"
  end
end

local_require.rb

require_relative 'mylib'

puts MyLib.hello("Ruby")

A plain require 'mylib' would fail unless the directory is in $LOAD_PATH; require './mylib' works only when the process runs from that directory. An absolute path can also be passed directly, as in require File.expand_path('mylib', __dir__).

Return Value and Load Errors

require returns true when it loads a feature and false when that feature is already loaded. A missing file raises LoadError instead of returning false.

require_value.rb

puts require 'json'   # true
puts require 'json'   # false

begin
  require 'missing_library'
rescue LoadError => e
  puts "Not available: #{e.message}"
end

The first call loads JSON and returns true; the second finds it in $LOADED_FEATURES and returns false. The rescue clause handles the missing library. Errors raised inside an existing file, such as NameError, propagate normally.

Requiring Gems

RubyGems integrates with require to load installed gems. This example shows requiring a popular HTTP library.

gem_require.rb

require 'httparty'

response = HTTParty.get('https://api.github.com')
puts response.code

After installing the gem (gem install httparty), we can require it like any standard library. RubyGems finds the installed gem and adds its lib directory to the load path when the gem is activated.

Conditional Requiring

We can conditionally require different implementations based on environment. This example loads either a production or development database adapter.

conditional_require.rb

if ENV['RACK_ENV'] == 'production'
  require 'pg'
else
  require 'sqlite3'
end

The code checks an environment variable to determine which database library to load. The selected adapter gem must be installed; a missing gem raises LoadError.

Requiring Multiple Files

Large projects often split code across multiple files. This example shows requiring several related files from a directory.

multi_require.rb

Dir.glob(File.join(__dir__, 'lib', '*.rb')).sort.each do |file|
  require file
end

The code builds absolute paths with __dir__, so it works regardless of the current directory. Sorting makes the load order deterministic. A bare relative path such as lib/a.rb would fail by default because the current directory is not in $LOAD_PATH.

Requiring with Load Path Modification

Sometimes we need to add custom paths to $LOAD_PATH before requiring. This example shows how to properly modify the load path.

load_path_require.rb

$LOAD_PATH.unshift(File.expand_path('vendor', __dir__))
require 'custom_lib'

puts CustomLib.version

The code adds the vendor directory next to the current file to $LOAD_PATH before requiring. unshift puts it first, so its files take precedence. Here vendor/custom_lib.rb defines CustomLib.version.

Source

Ruby Require Documentation

This tutorial covered Ruby's require method with practical examples showing library loading, local files, gems, and path management techniques.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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