How does Ruby know where to find a required file?

Question

Here is one more newbie question:

require 'tasks/rails'

I saw this line in Rakefile in the root path of every rails project. I guess this line is used to require vendor/rails/railties/lib/tasks/rails.rb to get all rake tasks loaded:

$VERBOSE = nil
# Load Rails rakefile extensions
Dir["#{File.dirname(__FILE__)}/*.rake"].each { |ext| load ext }
# Load any custom rakefile extensions
Dir["#{RAILS_ROOT}/lib/tasks/**/*.rake"].sort.each { |ext| load ext }
Dir["#{RAILS_ROOT}/vendor/plugins/*/**/tasks/**/*.rake"].sort.each { |ext| load ext }

My question is why only 'tasks/rails' is specified for the require method, but not the full path of the file?

Thanks in advance.

Answer 1

When you start your rails app it runs config/boot.rb which calls Rails::Initializer.set_load_path and thatsets up the $LOAD_PATH.

Ruby uses that list of directories to find the files specified on a require line. If you give it an absolute path like require '/home/lolindrath/ruby/lib.rb' it will skip that search.

This is roughly analogous to #include <stdlib.h> in C/C++ where it searches the include path you give the compiler to find that header file.