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"
require_relative is a convenient subset of require
require_relative('path')
equals:
require(File.expand_path('path', File.dirname(__FILE__)))
if __FILE__ is defined, or it raises LoadError otherwise.
This implies that:
require_relative 'a' and require_relative './a' require relative to the current file (__FILE__).
This is what you want to use when requiring inside your library, since you don't want the result to depend on the current directory of the caller.
eval('require_relative("a.rb")') raises LoadError because __FILE__ is not defined inside eval.
This is why you can't use require_relative in RSpec tests, which get evaled.
The following operations are only possible with require:
require './a.rb' requires relative to the current directory
require 'a.rb' uses the search path ($LOAD_PATH) to require. It does not find files relative to current directory or path.
This is not possible with require_relative because the docs say that path search only happens when "the filename does not resolve to an absolute path" (i.e. starts with / or ./ or ../), which is always the case for File.expand_path.
The following operation is possible with both, but you will want to use require as it is shorter and more efficient:
require '/a.rb' and require_relative '/a.rb' both require the absolute path.
Reading the source
When the docs are not clear, I recommend that you take a look at the sources (toggle source in the docs). In some cases, it helps to understand what is going on.
require:
VALUE rb_f_require(VALUE obj, VALUE fname) {
return rb_require_safe(fname, rb_safe_level());
}
require_relative:
VALUE rb_f_require_relative(VALUE obj, VALUE fname) {
VALUE base = rb_current_realfilepath();
if (NIL_P(base)) {
rb_loaderror("cannot infer basepath");
}
base = rb_file_dirname(base);
return rb_require_safe(rb_file_absolute_path(fname, base), rb_safe_level());
}
This allows us to conclude that
require_relative('path')
is the same as:
require(File.expand_path('path', File.dirname(__FILE__)))
because:
rb_file_absolute_path =~ File.expand_path
rb_file_dirname1 =~ File.dirname
rb_current_realfilepath =~ __FILE__
Summary
Use require for installed gems
Use require_relative for local files
require uses your $LOAD_PATH to find the files.
require_relative uses the current location of the file using the statement
require
Require relies on you having installed (e.g. gem install [package]) a package somewhere on your system for that functionality.
When using require you can use the "./" format for a file in the current directory, e.g. require "./my_file" but that is not a common or recommended practice and you should use require_relative instead.
require_relative
This simply means include the file 'relative to the location of the file with the require_relative statement'. I generally recommend that files should be "within" the current directory tree as opposed to "up", e.g. don't use
require_relative '../../../filename'
(up 3 directory levels) within the file system because that tends to create unnecessary and brittle dependencies. However in some cases if you are already 'deep' within a directory tree then "up and down" another directory tree branch may be necessary. More simply perhaps, don't use require_relative for files outside of this repository (assuming you are using git which is largely a de-facto standard at this point, late 2018).
Note that require_relative uses the current directory of the file with the require_relative statement (so not necessarily your current directory that you are using the command from). This keeps the require_relative path "stable" as it always be relative to the file requiring it in the same way.
From Ruby API:
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.
When you use require to load a file,
you are usually accessing
functionality that has been properly
installed, and made accessible, in
your system. require does not offer a
good solution for loading files within
the project’s code. This may be useful
during a development phase, for
accessing test data, or even for
accessing files that are "locked" away
inside a project, not intended for
outside use.
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"
Since neither
"test" nor "test/data" are likely to
be in Ruby’s library path (and for
good reason), a normal require won’t
find them. require_relative is a good
solution for this particular problem.
You may include or omit the extension
(.rb or .so) of the file you are
loading.
path must respond to to_str.
You can find the documentation at http://extensions.rubyforge.org/rdoc/classes/Kernel.html
The top answers are correct, but deeply technical. For those newer to Ruby:
require_relative will most likely be used to bring in code from another file that you wrote.
for example, what if you have data in ~/my-project/data.rb and you want to include that in ~/my-project/solution.rb? in solution.rb you would add require_relative 'data'.
it is important to note these files do not need to be in the same directory. require_relative '../../folder1/folder2/data' is also valid.
require will most likely be used to bring in code from a library someone else wrote.
for example, what if you want to use one of the helper functions provided in the active_support library? you'll need to install the gem with gem install activesupport and then in the file require 'active_support'.
require 'active_support/all'
"FooBar".underscore
Said differently--
require_relative requires a file specifically pointed to relative to the file that calls it.
require requires a file included in the $LOAD_PATH.
I just saw the RSpec's code has some comment on require_relative being O(1) constant and require being O(N) linear. So probably the difference is that require_relative is the preferred one than require.
I want to add that when using Windows you can use require './1.rb' if the script is run local or from a mapped network drive but when run from an UNC \\servername\sharename\folder path you need to use require_relative './1.rb'.
I don't mingle in the discussion which to use for other reasons.
absolute path
require './app/example_file.rb'
shortened name
require_relative 'example_file'
I have written a few ruby classes. However, when trying to access one from another directory I am getting the following error:
uninitialized constant Main::AppVersion
This is what the directory structure looks like:
home --> a --> app_version.rb
home --> b --> c --> lib --> main.rb (and other classes)
Everything within "lib" can see each other. However, when trying to access app_version, it fails. I added the path to app version (home/a) to the $LOAD_PATH. So it should be available from there. I have also tried "requiring" my other class, but when I do that I get the following error:
LoadError: no such file to load -- AppVersion
Any idea on what I could be doing wrong here would be highly appreciated. Thanks!
Can try using require_relative:
require_relative '../../../a/app_version'
You error is:
LoadError: no such file to load -- AppVersion
So require is looking for a file AppVersion.rb. And you said the file name is app_version.rb. Try to load it with:
require 'app_version'
after setting up the $LOAD_PATH.
When you define Main::AppVersion class it's supposed to reside in main folder (i.e. main/app_version.rb)
So it doesn't depend on $LOAD_PATH.
You will have to require the file.
LoadError: no such file to load -- AppVersion
Do you require "app_version" ? Or require "AppVersion"? (first one is correct, and consider to require_relative)
Another option is to run ruby and give the include path like
ruby -Ia -Ib/c/lib b/c/lib/main.rb
.
I have a Ruby app that runs on a server with no web interface. It is run using the command line(ruby path/to/file.rb).
I have classes in different files that I want to be accessible. The files are located in the "app/classes" directory.
I put this in the application.rb file:
config.autoload_paths += Dir["#{config.root}/classes"]
and I get an uninitialized constant error.
I can put in "require_relitive 'somefile'" but I would rather not have to do this for every class that is used. How do I create an autoload path and where should it be located at?
Use require_all
See https://github.com/jarmo/require_all
It basically allows you to write this:
require 'require_all'
require_all 'app/classes'
And all ruby files in app/classes will be loaded.
I have the following structure
tests
specific tests
first_test.rb
more tests
second_test.rb
test_helper.rb
Now I am trying to require test_helper in both first_test and second_test. The following works
require '../test_helper.rb'
and from command line I should be under specific tests and execute
ruby first_test.rb
How can I get more flexibility ie. I want to be in any directory and execute these tests. Currently I am getting 'no such file'. This is not a rails app but in rails I could simply do require 'test_helper.rb'
Bonus points for making this work with rake.
Put your test_helper and other helpers in a separate directory like
/home/XXX/projects/test_project/lib/
or wherever you like and use base directory like
Dir["base/path/to/your/helper/*.rb"].each {|file| require file }
or from my above example
Dir["/home/XXX/projects/test_project/lib/*.rb"].each {|file| require file }
Thats it.
Now add this line to the beginning of every test you want to run separately from any directory.And forget about the directory issue.
I am writing a Ruby script which was supposed to be a small thing but has grown quite large, way to large to have everything crammed into one source file. So I am trying to separate the project into different files. I have four classes and I want to put each in its own separate source file.
What I did:
I moved all of the classes into their own files so now I have this
proj/GoogleChart.rb
proj/BarChart.rb
proj/PieChart.rb
proj/GroupedBarChart.rb
Now that they are in other files I am getting uninitialized constant GoogleChart (NameError) in all of my subclasses on the line where I inherit from GoogleChart, i.e.
require 'GoogleChart'
BarChart < GoogleChart
Can anyone tell me what is wrong?
Thanks
EDIT
Using ruby version 1.8.4
Also I have tried using the absolute path:
require 'C:/Documents and Settings/proj/GoogleChart.rb' and this is still producing a NameError
In Ruby 1.8.x, the . is part of your load path. So you should at least try to debug that by including something like:
puts $:
require 'GoogleChart'
class BarChart < GoogleChart
end
and load that in an IRB session:
Open the session in your directory proj.
Enter there require 'BarChart'
Look at the result.
For me it is:
c:\apps\ruby\test\proj>irb
irb(main):001:0> require 'BarChart'
C:/Users/mliebelt/.pik/rubies/Ruby-187-p334/lib/ruby/site_ruby/1.8
C:/Users/mliebelt/.pik/rubies/Ruby-187-p334/lib/ruby/site_ruby/1.8/i386-msvcrt
C:/Users/mliebelt/.pik/rubies/Ruby-187-p334/lib/ruby/site_ruby
C:/Users/mliebelt/.pik/rubies/Ruby-187-p334/lib/ruby/vendor_ruby/1.8
C:/Users/mliebelt/.pik/rubies/Ruby-187-p334/lib/ruby/vendor_ruby/1.8/i386-msvcrt
C:/Users/mliebelt/.pik/rubies/Ruby-187-p334/lib/ruby/vendor_ruby
C:/Users/mliebelt/.pik/rubies/Ruby-187-p334/lib/ruby/1.8
C:/Users/mliebelt/.pik/rubies/Ruby-187-p334/lib/ruby/1.8/i386-mingw32
.
=> true
So the require is successful for me, and the . is part of the path (as it should). As you can see, I am working with Ruby 1.8.7, I don't know if anything has changed since 1.8.4 that is relevant here.
So please describe exactly how you run your file:
Have you opened a shell to run the file?
What is the current working directory of that shell?
Do you run by double-clicking it?
It only works when you are in your proj directory and run there (with ruby in your shell path) ruby BarChart.rb.