Why

Load path simply refers to:

Where to look for things.

For Ruby, global variable $LOAD_PATH is an array containing all the paths. It’s defined when Ruby starts the program.

Check out this article for a good basic explanation.

What

How

We can check the default load path of our Ruby installation with ruby -e 'puts $LOAD_PATH'.

/Users/rayman/.gem/ruby/3.1.2/gems/error_highlight-0.6.0/lib
/Users/rayman/.rubies/ruby-3.1.2/lib/ruby/site_ruby/3.1.0
/Users/rayman/.rubies/ruby-3.1.2/lib/ruby/site_ruby/3.1.0/arm64-darwin21
/Users/rayman/.rubies/ruby-3.1.2/lib/ruby/site_ruby
/Users/rayman/.rubies/ruby-3.1.2/lib/ruby/vendor_ruby/3.1.0
/Users/rayman/.rubies/ruby-3.1.2/lib/ruby/vendor_ruby/3.1.0/arm64-darwin21
/Users/rayman/.rubies/ruby-3.1.2/lib/ruby/vendor_ruby
/Users/rayman/.rubies/ruby-3.1.2/lib/ruby/3.1.0
/Users/rayman/.rubies/ruby-3.1.2/lib/ruby/3.1.0/arm64-darwin21

Notice, Rails application has way more paths than above.

Where

When you call require ‘x’, this is what happens:

1. If the file can be loaded from the existing Ruby $LOAD_PATH, load as it is.
2. Otherwise, installed gems are searched first file that matches. If it’s found in gem ‘y’, that gem is added to the $LOAD_PATH.

When require_relative ‘x’ is called, Ruby tries to load the file relative to the directory containing the requiring file.

When

Who