Read knob files with facter for puppet

I found myself recently writing yet another fact to read the contents of a knob file, so I generalized one to read all the files found in /etc/knobs and return the contents as facts named after the files found.

Caveats: read_knobs.rb returns only the last line it finds in the file. This is on purpose. It also skips all lines beginning with # so you can use shell-style comments. Files that are empty create facts with the value true, and files containing just a t or f are normalized to true or false respectively.

Here's the source, and it's also available on github.

#!/usr/bin/ruby
#
# fact returns knob values based on contents of /etc/knobs.
#
# Author: jpb@ooyala.com
#
# Copyright 2009 Ooyala, Inc.
#
#   Licensed under the Apache License, Version 2.0 (the "License");
#   you may not use this file except in compliance with the License.
#   You may obtain a copy of the License at
#
#       http://www.apache.org/licenses/LICENSE-2.0
#
#   Unless required by applicable law or agreed to in writing, software
#   distributed under the License is distributed on an "AS IS" BASIS,
#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#   See the License for the specific language governing permissions and
#   limitations under the License.
#
require 'facter'
def logger(message)
  system("/usr/bin/logger -t read_knobs #{message}")
end
# facts can only have one value. We ignore lines with shell style comments,
# and return the last valid line.
def read_knob(filename)
  knob_name = filename.split('/')[-1]
  knob_file = File.open(filename)
  # an empty knob file must have been created for a reason, so set default
  # value to true
  value = true
  knob_file.each { |line|
    if line[0,1] != "#"
      if (line.downcase.chomp == "true") or (line.downcase.chomp == "t")
        value = true
      elsif (line.downcase.chomp == "false") or (line.downcase.chomp == "f")
        value = false
      else
        value = line.chomp
      end
    end
  }
  knob_file.close
  value
end
def load_knobs(knob_d)
  logger "Processing #{knob_d}..."
  if ! File.directory?(knob_d)
    logger("Can't read #{knob_d}!")
    return nil
  end
  Dir["#{knob_d}/*"].each do |knob|
    if File.readable?(knob)
      knob_name = knob.split('/')[-1]
      Facter.add("#{knob_name}") do
        setcode do
          data = read_knob(knob)
          data
        end
      end
    else
      logger("Can't read #{knob}!")
    end
  end
end
load_knobs('/etc/knobs')