File, Pathname, Dir

http://www.ruby-doc.org/core/classes/File.html
http://www.ruby-doc.org/core/classes/Pathname.html
http://www.ruby-doc.org/core/classes/Dir.html#M002347

join, dirname, __FILE__, RAILS_ROOT, directory?

require File.join(File.dirname(__FILE__), 'boot')

RAILS_ROOT = "#{File.dirname(__FILE__)}/.." unless defined?(RAILS_ROOT)


>> File.directory?("#{RAILS_ROOT}/app")
=> true
>> File.exist?("#{RAILS_ROOT}/app")
=> true

>> File.exist?("#{RAILS_ROOT}/app/controllers/application.rb")
=> true
>> File.directory?("#{RAILS_ROOT}/app/controllers/application.rb")
=> false

Dir is file, too


  Dir["config.?"]                     #=> ["config.h"]
  Dir.glob("config.?")                #=> ["config.h"]
  Dir.glob("*.[a-z][a-z]")            #=> ["main.rb"]
  Dir.glob("*.[^r]*")                 #=> ["config.h"]
  Dir.glob("*.{rb,h}")                #=> ["main.rb", "config.h"]
  Dir.glob("*")                       #=> ["config.h", "main.rb"]
  Dir.glob("*", File::FNM_DOTMATCH)   #=> [".", "..", "config.h", "main.rb"]