Quick tricks to expand load paths in ruby

ruby_files_in_load_paths.rb

# expand_path is genuine and DOES KNOW ABOUT absolute and relative paths
File.expand_path('relative/path/to/dir_or_file', '/start/path') # "/start/path/relative/path/to/dir_or_file"
File.expand_path('../application', __FILE__) # "/absolute/path/to/FILE/../application"
File.expand_path('/path/to/dir_or_file', '/start/path') # "/path/to/dir_or_file"
File.expand_path('../path/to/dir_or_file', '/start/path') # "/start/path/to/dir_or_file"

# join seems to be STUPID. It just joins strings (and adds file separator if needed)
File.join('some/path/', '/other/path.rb') # "some/path/other/path.rb"

# modify the global load path:
$: #actual load path
$:.unshift(File.expand_path('../lib', __FILE__))
$:.unshift('path/to/dir') #insert some directory to loadpath
$:.unshift(File.expand_path('test', Rails.root)) # add test directory to the load paths

# require (load) a file into the environment
require File.expand_path('../../config/environment', __FILE__)  # in fact we are using absolute path here
require 'relative_path/file' # the whole load path is checked