gistfile1.rb

# app_config.yml
# --------------
# development:
#   env: dev
#   server: dev.domain.com
# production:
#   env: prod
#   server: prod.domain.com
#
# local_override.yml
# ------------------
# server: localhost
# new_value: blah

AppConfig = ApplicationConfig.new("app_config.yml")
AppConfig.use_environment!("development", :override_with => "local_override.yml")

AppConfig.env
# => "dev"

AppConfig.server
# => "localhost"

AppConfig.new_value
# => "blah"