Is Require File.Expand_Path(..., _File_) the Best Practice

Is require File.expand_path(..., __FILE__) the best practice?

In Ruby 1.9.2 + require_relative is probably the more correct way to do it.

require was changed to not include your '.' directory for security reasons. require_relative was added to provide a local-file solution for modules relative to your calling script's path.

You can search here on StackOverflow, particularly in "What is require_relative in Ruby?", and the internets and find usage tricks and the why-for messages explaining how it came about.

File.expand_path(../../Gemfile, __FILE__) How does this work? Where is the file?

File.expand_path('../../Gemfile', __FILE__)

is a somewhat ugly Ruby idiom for getting the absolute path to a file when you know the path relative to the current file. Another way of writing it is this:

File.expand_path('../Gemfile', File.dirname(__FILE__))

both are ugly, but the first variant is shorter. The first variant is, however, also very non-intuitive until you get the hang of it. Why the extra ..? (but the second variant may give a clue as to why it is needed).

This is how it works: File.expand_path returns the absolute path of the first argument, relative to the second argument (which defaults to the current working directory). __FILE__ is the path to the file the code is in. Since the second argument in this case is a path to a file, and File.expand_path assumes a directory, we have to stick an extra .. in the path to get the path right. This is how it works:

File.expand_path is basically implemented like this (in the following code path will have the value of ../../Gemfile and relative_to will have the value of /path/to/file.rb):

def File.expand_path(path, relative_to=Dir.getwd)
  # first the two arguments are concatenated, with the second argument first
  absolute_path = File.join(relative_to, path)
  while absolute_path.include?('..')
    # remove the first occurrence of /<something>/..
    absolute_path = absolute_path.sub(%r{/[^/]+/\.\.}, '')
  end
  absolute_path
end

(there's a little bit more to it, it expands ~ to the home directory and so on -- there are probably also some other issues with the code above)

Stepping through a call to the code above absolute_path will first get the value /path/to/file.rb/../../Gemfile, then for each round in the loop the first .. will be removed, along with the path component before it. First /file.rb/.. is removed, then on the next round /to/.. is removed, and we get /path/Gemfile.

To make a long story short, File.expand_path('../../Gemfile', __FILE__) is a trick to get the absolute path of a file when you know the path relative to the current file. The extra .. in the relative path is to eliminate the name of the file in __FILE__.

In Ruby 2.0 there is a Kernel function called __dir__ that is implemented as File.dirname(File.realpath(__FILE__)).

Requiring files in Ruby

require_relative 'lib/checkers/board'
require_relative 'lib/checkers/checker'

This is how I have always done it. This is located in my main app file, which is always in the root directory. I'm unsure how it will behave from other files, although I believe it will be relative to the calling file.

Also, settings.root will return the root directory of your app, no need for File.dirname(__FILE__) anywhere.

This works in Ruby 1.9 without any special techniques via the comments above.

If you are using 1.8, you can do this

require './lib/checkers/board'
require './lib/checkers/checker'

Other techniques for 1.8 are listed in this question.

Best way to require all files from a directory in ruby?

How about:

Dir["/path/to/directory/*.rb"].each {|file| require file }

What does __FILE__ mean in Ruby?

It is a reference to the current file name. In the file foo.rb, __FILE__ would be interpreted as "foo.rb".

Edit: Ruby 1.9.2 and 1.9.3 appear to behave a little differently from what Luke Bayes said in his comment. With these files:

# test.rb
puts __FILE__
require './dir2/test.rb'

# dir2/test.rb
puts __FILE__

Running ruby test.rb will output

test.rb
/full/path/to/dir2/test.rb

understanding __FILE__

Since you are using a relative path in '../../views', you need a reference point to expand the path. The second argument, which happens to be __FILE__ in this case, overrides the default reference point, which is the current working directory.

Ruby Doc File.expand_path

What is the difference between require_relative and require in Ruby?

Just look at the docs:

require_relative complements the builtin method require by allowing you to load a file that is relative to the file containing the require_relative statement.

For example, if you have unit test classes in the "test" directory, and data for them under the test "test/data" directory, then you might use a line like this in a test case:

require_relative "data/customer_data_1"

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