Rails.env vs RAILS_ENV

ENV['RAILS_ENV'] is now deprecated.

You should use Rails.env which is clearly much nicer.

According to the docs, #Rails.env wraps RAILS_ENV:

    # File vendor/rails/railties/lib/initializer.rb, line 55
     def env
       @_env ||= ActiveSupport::StringInquirer.new(RAILS_ENV)
     end

But, look at specifically how it's wrapped, using ActiveSupport::StringInquirer:

Wrapping a string in this class gives you a prettier way to test for equality. The value returned by Rails.env is wrapped in a StringInquirer object so instead of calling this:

Rails.env == "production"

you can call this:

Rails.env.production?

So they aren't exactly equivalent, but they're fairly close. I haven't used Rails much yet, but I'd say #Rails.env is certainly the more visually attractive option due to using StringInquirer.

Before Rails 2.x the preferred way to get the current environment was using the RAILS_ENV constant. Likewise, you can use RAILS_DEFAULT_LOGGER to get the current logger or RAILS_ROOT to get the path to the root folder.

Starting from Rails 2.x, Rails introduced the Rails module with some special methods:

• Rails.root
• Rails.env
• Rails.logger

This isn't just a cosmetic change. The Rails module offers capabilities not available using the standard constants such as StringInquirer support. There are also some slight differences. Rails.root doesn't return a simple String buth a Path instance.

Anyway, the preferred way is using the Rails module. Constants are deprecated in Rails 3 and will be removed in a future release, perhaps Rails 3.1.