Query puppet configuration from a file

puppet_config.rb

module Puppet::Parser::Functions
  newfunction(:puppet_config, :type => :rvalue, :doc => <<-EOS
This function queries Puppet configuration files.

*Examples:*

    puppet_config('/etc/puppetlabs/installer/answers.install', 'q_install')

Will return: 'y'

Note that the pe-puppet user must be able to read the file.
    EOS
  ) do |arguments|

    # Technically we support two arguments but only first is mandatory ...
    raise(Puppet::ParseError, "puppet_config(): Wrong number of arguments " +
      "given (#{arguments.size} for 2)") if arguments.size < 2

    filename = arguments[0]

    unless filename.is_a? String
      raise Puppet::ParseError "puppet_config(): expected first argument to be a String, got #{filename.inspect}"
    end

    # unless Puppet::FileSystem.exist?(filename)
    #   raise Puppet::ParseError "puppet_config(): file #{filename} does not exist"
    # end

    key      = arguments[1]

    unless key.is_a? String
      raise Puppet::ParseError "puppet_config(): expected second argument to be a String, got #{key.inspect}"
    end

    default  = arguments[2]
    if default
      unless default.is_a? String
        raise Puppet::ParseError "puppet_config(): expected third argument to be a String, got #{default.inspect}"
      end
    else
      default = ''
    end

    parser = Puppet::Parser::Parser.new(environment)
    parser.watch_file(filename)

    config = IO.readlines(filename)
    match  = config.detect{ |line| line.match(/^\s*#{key}\s*=\s*/) }

    if (match != :Null)
      return match.sub(/^\s*#{key}\s*=\s*/, '').sub(/\n$/, '')
    else
      return default
    end

  end
end