Rails 3.x initializer for loading HEROKU envs in local environment

load_heroku_env.rb

# Load heroku ENV variables in local development on Rails startup
#
# For a variable defined like this:
#
#      heroku config:add S3_KEY='s3krit'
#
# This initializer will define a ENV["S3_KEY"] with a 's3krit' value in development environment.

# Be careful to not overwrite any variable by mistake. 
# Potentially destructive.

if Rails.env.development?
  require 'heroku/command/config'
  
  app_name = Rails.application.class.parent_name.downcase
  heroku_env = Heroku::Command::Base.new.heroku.config_vars(app_name)
  
  # Copy manually. Can't merge since ENV is not a real hash
  heroku_env.keys.each do |key|
    ENV[key]=heroku_env[key]
  end
end