a.rb

require 'yaml'

module Mailbosa
  class Settings
    Path = [
      '/home/renich/Projects/ruby/mailbosa/usr/local/etc/mailbosa/settings.yml',
      '/home/renich/Projects/ruby/mailbosa/etc/mailbosa/settings.yml'
    ]

    def initialize
      file = Path.select { |path| File.exists? path }
      @settings = self.read( file.first )
    end

    def read( file )
      YAML.load_file( file ).to_hash
    end

    def [](key)
      @settings[key]
    end
  end
end

s = Mailbosa::Settings.new

p s[:key]