Question

I have a command line utility written in Ruby using GLI framework. I would like to have configuration for my command line utility in my home directory, using Ruby itself as DSL to handle it (similar to Gemfile or Rakefile).

I have in class ConfigData in folder lib/myapp. The class looks like following way:

class ConfigData
  @@data = {}

  class ConfigItem
    def initialize
      @data = {}
    end
    def missing_method(name, *args)
      @data[name] = args[0]
    end
  end

  def self.add(section)
    item = ConfigItem.new()
    yield item
    @@data[section]=item
  end

end

Now, what I would like to have, is the config file, preferrably with name Myappfile, in current working folder, with the following content

add('section1') do |i|
  i.param1 'Some data'
  i.param2 'More data'
end

When this code was included between class and end of ConfigData, it worked fine. But now I would like to have it placed in the working folder, where I start the application.

I tried require(‘./Myappfile’) between class and end of ConfigData, but it doesn’t work for me. I tried to read the source codes of rake, but it is not very much clear to me.

Any hint how this can be solved?

Answer 1

To evaluate code within the context of an instance, which is what you want to do, you need the instance_eval() method. Never, ever, use normal eval. Ever. Anyway, here’s how you’d load your fingi file and get the data:

config = ConfigData.new
config.instance_eval(File.read("Myconfig"))
#Access configuration data here from the config object

That simple. After you’ve loaded the object in that way, you can access values of the object.

WARNING: This is not very secure. This is actually a gaping security hole. Here’s the secure version:

f = Fiber.new {str = File.read("Myconfig"); $SAFE = 4; config = ConfigData.new; config.instance_eval(str); Fiber.yield config}
confdata = f.resume
#Access configuration data here from confdata.

This executes the external code in a (sort of) sandbox, so that it can’t do anything dastardly.

---

Also, why don’t you just use a YAML config? Unless configuration needs to run code like pwd or access RUBY_VERSION, YAML is much simpler and more secure, in addition to being more failproof.