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Create and manage configuration files in Ruby for Ruby. Jeckyl can be used to create a parameters hash from a simple config file written in Ruby, having run whatever checks you want on the file to ensure the values passed in are valid. All you need to do is define a class inheriting from Jeckyl, methods for each parameter, its default, whatever checking rules are appropriate and even a comment for generating templates etc. This is then used to parse a Ruby config file and create the parameters hash. Jeckyl comes complete with a utility to check a config file against a given class and to generate a default file for you to tailor. Type 'jeckyl readme' for more information.


>= 0.0.6
 Project Readme


Jeckyl is a versatile configuration file manager. It provides a simple way of defining and checking configuration parameters (including defaults) that can then be written as ruby in a config file. It can also be used to add/override parameters from the command line (using optparse) or even on the fly through an API. It comes with a handy utility that can generate a default config file, with comments, from the defined config class and check existing config files. It even creates a markdown file from the config class to make documentation easier.

Jeckyl can be used for simple parameters or complex structures with multiple calls. It provides a single place to define and check all inputs so that you don't have to include any parameter checking anywhere else in your code. Classes can be inherited to add further parameters, and the config file generated by the jeckyl command is conveniently divided to reflect this. Config files can also be merged so that multiple config files can be used (e.g. local/per-user/system).




Jeckyl was inspired by the configuration file methods in Unicorn.


Jeckyl comes as a gem. It can be installed in the usual way:

gem install jeckyl

That is practically all you need to do. Type 'jeckyl' to see usage and references to documentation.

Otherwise start coding your jeckyl config file.

Getting Started

To use Jeckyl, create a new parameter class and add a parameter method for each parameter you want to define in your config files. Think of the name of a parameter and prefix this with configure_:

require 'jeckyl'

class MyConfig < Jeckyl::Config

  def configure_my_greeting(greet)
    default "Hello"
    comment "Set the standard greeting for this application"

The parameter method first sets a default value to be used if no value is given at all in the config file. This is optional. It then describes the parameter, which is used by jeckyl when generating a blank config or a markdown file. Finally it runs a check on the given parameter to ensure it is a string. Note the name of the method that you use in the config file itself would be just 'my_greeting' wheras the parameter method is 'configure_my_greeting'.

Jeckyl comes complete with a whole range of checking methods that can be used for defining parameters (see {Jeckyl::Config} for details). These methods are handy because they handle errors transparently. It is not necessary, however, to use them so long as the value returned by the parameter method is what you want in your config hash.

To use this simple example, you can generate a config file with jeckyl:

$ jeckyl generate config lib/my_app/my_config.rb >test/conf.d/test.rb

This will produce something like:

# Set the standard greeting for this application
#my_greeting "Hello"

Which you could change to:

# Set the standard greeting for this application
my_greeting "Welcome"

And then, to use this config file to create the options hash:

require 'my_app/my_config'

options ='test/conf.d/test.rb')

options.inspect => {:config_files=>['test/conf.d/test.rb'], :my_greeting=>'Welcome'}

Using Jeckyl

Example Parameter Methods

Some examples of different parameters are given here, taken from the Jellog::Config class, Jellog being a jazzed-up ruby logger:

def configure_log_level(lvl)
  default :system
  comment "Controls the amount of logging done by Jellog",
    " * :system - standard message, plus log to syslog",
    " * :verbose - more generous logging to help resolve problems",
    " * :debug - usually used only for resolving problems during development",

  lvl_set = [:system, :verbose, :debug]
  a_member_of(lvl, lvl_set)


This shows a multi-line comment, the comment method takes any number of arguments and outputs them one per line. It also shows how to test that a key value is used that belongs to a set.

def configure_log_rotation(int)
  default 2
  comment "Number of log files to retain at any time, between 0 and 20"

  a_type_of(int, Integer) && in_range(int, 0, 20)


This shows how multiple tests can be and'd together.

def configure_log_length(int)
  default 1 #Mbyte
  comment "Size of a log file (in MB) before switching to the next log, upto 20 MB"

  a_type_of(int, Integer) && in_range(int, 1, 20)
  int * 1024 * 1024

This shows how the return value can be computed from the input parameter if required.

This final example shows a complicated parameter method that accepts an options hash and can be called multiple times:

def configure_sensors(options)
  comment "Add a sensor to monitor etc. This can be called multiple times",
    " ",
    " Sensors must be defined with the following:",
    "   :device - name of a device previously added with add_device",
    "   :name - the name for this thermostat (e.g. name of the room being monitored)",
    " ",
    " Sensors can have the following options:",
    "   :slope - gradient of the residual error function for the given sensor, default 0.0",
    "   :intercept - from the residual error function, default 0.0",
    " "

  unless @sensors
    @sensors =

  # remember the sensor names
  unless @names
    @names =

  unless options.has_key?(:device)
    raise Jeckyl::ConfigError, "You must supply a :device for each sensor"
  unless @devices.include?(options[:device])
    raise Jeckyl::ConfigError, "You must name a device that has already been added"
  unless options.has_key?(:name)
    raise Jeckyl::ConfigError, "You must supply a :name for each sensor"
  @sensors.each do |sensor|
    raise Jeckyl::ConfirError, "Each name must be unique" if sensor[:name] == options[:name]
  a_type_of(options[:name], String)

  raise Jeckyl::ConfigError, "You must supply an index" unless options.has_key?(:index)
  a_type_of(options[:index], Integer) && in_range(options[:index], 1, 4)

  options[:slope] ||= 0.0
  a_type_of(options[:slope], Float)

  options[:intercept] ||= 0.0
  a_type_of(options[:intercept], Float)

  @names << options[:name]

  @sensors << options # return the current array of sensors


The method uses its own instance variables to keep track of things over multiple calls and returns the @sensors array so that the actual parameter returned from Jeckyl will be the last value returned. It uses a mixture of jeckyl tests and explicit tests to ensure the parameters are correct. If preferred, you can add custom helper methods to your parameter class in the same manner as {Jeckyl::Config}.

Writing Ruby

Because the config file is ruby, it can contain any valid ruby code to help construct your parameters, which can be instances of complex classes if required. BUT this also means the code can do things you might not have intended so some care is needed here!

One of the things you can add, if it helps, is your own checking method. Call it what you like, pass in the object to check (and whatever else you need) and either return the item or raise an error if the checks fail. There are two methods available: {Jeckyl::Config#raise_config_error} e.g. for defining a value outside the required range and {Jeckyl::Config#raise_syntax_error} e.g. for defining a string where a number is required.

Can't be bothered? a more relaxed approach

If you are lazy and cannot be bothered with defining lots of methods, you can relax the parsing and checking and convert a parameter file straight into an options hash. To relax checking, set the :relax option to true when creating the parameters hash. Then any parameter value pairs in the config file will be converted to key-value pairs in the hash without any checks at all. You obviously cannot do much with this approach but in simple cases it may be OK?

If you don't like having to prefix your parameter methods with 'configure_' you can set another prefix by redefining the prefix method in your subclass to return something else:

def prefix
  'set' # could also be 'cf' if you find typing a bore

Managing Parameter Hashes

You can easily merge parameter files using the {Jeckyl::Config#merge} method:

config ='/etc/system.rb')
config.merge(File.join(ENV[USER], '.my_config_.rb'))

Jeckyl includes a couple of methods to help sub-divide parameter hashes. To extract all of the parameters from a hash that belong to a given Jeckyl class, use Class.intersection(hash) (see {Jeckyl::Config.intersection}). And to remove all of the parameters from one config hash in another, use conf.complement(hash) ({Jeckyl::Config#complement}).

For example, the Jellog logger defines a set of logging parameters in Jellog::Config. These may be inherited by another service that adds its own parameters (such as Jerbil):

all_options =

log_opts = Jellog::Config.intersection(all_options)

jerb_opts = all_options.complement(log_opts)

Command Line Options - Jeckyl with Optparse

Jeckyl can also process command line options using optparse. This can be easily done by adding an option method call to your parameter method, which has the same parameters as optparse:

def configure_param_with_option(param)
  option_set = [:none, :some, :all]
  default :none
  comment "Sets the option type to be one of",
    "  :none - no options",
    "  :some - some options",
    "  :all - all options"
  describe "set the option type"
  option "-o", "--option Type", option_set
  a_member_of(param, option_set)

The {Jeckyl::Config#describe describe} method allows a short usage style description over the longer config-file comment, and the {Jeckyl::Config#option} method receives the same parameters as the optparse#on method less the description bit.

Adding this to your parameter method does not actually do anything without then parsing the options:

# create a config hash
opts =
# parse command-line options with the default ARGV

The {Jeckyl::Config#optparse optparse} method creates and Optparse object with the options defined in your parameter methods (ignoring those with no option set), adds a '-c' option for specifying a config file and a -h option for help. It also parses the results.

The {Jeckyl::Config#optparse optparse} method can also yield the real Optparse object into a block where you can add further options unrelated to Jeckyl. The parse! is done automatically when the block returns.

# parse them with some extra options added
opts.optparse do |opts|
  # receives the same methods as an optparse object
  opts.on('-p', '--pretend', 'Do not do anything for real') do
    @pretend = true
# parse! is done automatically at the end of the block

This does two things: it updates the parameters with option statements from the command line and it also adds the options in the block but independent of the config object itself.

A word about the -c option. This is really only added so that it is shown in the help results. The option is not used by the optparse method for fairly obvious reasons: the instance method is applied to a config hash so the config file has already been evaluated. To use the -c option you need to preprocess the command line with a class method:

# set the default config file
default_config_file = '/etc/my_app/config_file.rb'
# get the config options, if it exists
argv, config_file = MyConfig.get_config_opt(ARGV,default_config_file)
# now use the config file
@config =, config_file)

Note that {Jeckyl::Config.get_config_opt} returns the inputs if there is no option. And at this time it only looks for '-c', so the bit about '--config' is a lie!

Using Parameter methods on the fly

Jeckyl can also be used without a config file, for example as part of an API where the inputs are coded in. A config class and parameter methods are defined as usual, including defaults. On the inside of the API, where you might explicitly check inputs, you instead call the parameter method:

# somewhere, a default config hash is created
@config =

# later, this is used to check a parameter:
@param = @config.param_with_option(param)

# if the param does not match the config requirements then an exception is called

This allows you to blend in config files if required and command line options as well. The only messy bit is that your API will raise {Jeckyl::ConfigError} unless you trap this and then convert it to your own local exception.

Jeckyl::Config < Hash

Finally, note that {Jeckyl::Config} is itself a subclass of Hash, and therefore Jeckyl config objects inherit all hash methods as well!

The 'jeckyl' Command

Jeckyl comes with a simple script: bin/jeckyl to help in creating, checking and documenting parameters.

You can create a simple config class to start you off with:

$ jeckyl klass <name>

which will output a small template to stdout. By default this will inherit from {Jeckyl::Config} but you can add another parent with, for example:

$ jeckyl klass MyService JerbilService::Config

Save the file and edit it to add your parameters as required. Once you have defined the config class, you can generate a default config file for your application using:

$ jeckyl config path/to/config_class.rb

This will generate a config file on stdout for each of the parameters, with the comment defined in the parameter method and the default value where defined. Defaults will be commented out. You can save this file and edit it to create a new config file.

Where you have created a config class that inherits from another config class, you will probably want to create a config file with all of the parameters in it. By default only the config class defined in the given file will be generated. To generate all parameters add the -k (for concat) option:

$ jeckyl config path/to/config_class.rb -k

The resulting config file will be neatly divided into sections, one for each class, starting with the most ancestral. If you want to know what config classes you have inherited, then try:

$ jeckyl list path/to/config_class.rb

This will output an indexed list of the classes available. If you wanted to generate a config file just for one class, select it with the -C option and the index from the list:

$ jeckyl config path/to/config_class.rb -C 2

Once you have editted your config file you can check if it is OK:

$ jeckyl check path/to/config_class.rb path/to/config_file.rb

This will either display error messages or tell you that the config file is OK.

Having created a config class, you may want to document it. Given that each parameter is already described within the parameter method, it would be inconvenient to have to copy these comments into ruby comments just to help the various documentation tools around. Instead, you can generate a markdown file from the parameter methods and then include this in your documentation:

$ jeckyl markdown path/to/config_class.rb

This task takes the same options as the config task. You can then include a reference or link to this file in the header comment for your config class. The template generated above already has a yard @see directive.

# @see file:lib/project/

Code Walkthrough

Jeckyl is documented on

Jeckyl consists of a single class: {Jeckyl::Config}. When you create an instance of a subclass the following happens (see {Jeckyl::Config#initialize}):

  • all of the parameter methods are called by {Jeckyl::Config#get_defaults} to obtain their default values (the {Jeckyl::Config#default default} method sets this in a hash) and are called again with these default values to process them through whatever the parameter method defines. This ensures, for example, that if the parameter is multiplied by 10 before being added to the config hash, the default value is also multipled by 10.

  • if no config file is provided, the default values are returned as the options hash. This is used, for example, by the config {Jeckyl::Config.generate_config generator}.

  • finally, the given config file (whose name is added to the hash) is evaluated so that the resulting parameters are added, overriding any defaults or manually entered values.

All of this is done with just a little bit of meta-magic. When the config file is eval'ed the parameter names are eval'ed in the context of the instance being created, but because the parameter methods are all prefixed with something (configure by default) method_missing is called instead. This orchestrates the setting of parameters and collecting of results into the options hash, passing the parameter values to the corresponding parameter method.

For example, a config file might contain:

# define a greeting for the application
greeting "Hello"

There is no greeting method, so method_missing is called instead. This remembers the name of the "missing" method (:greeting), calls configure_greeting and stores the results in the instance's hash. The main reason for doing this (as opposed to just calling the method 'greeting') is to enable the evaluation of defaults and comments in the context of each parameter method. All of this is private and therefore under the bonnet.


See the {file:Gemfile} for details of dependencies.

Tested on Ruby 1.9.3_p547 and 2.0.0_p481 (Gentoo 2.1 not yet unmasked at time of writing - Oct 2014). Tested with RSpec 3.1.0 - see below.

Testing Jeckyl

There is an rspec test file to test the whole thing (spec/jeckyl_spec.rb). It uses the test subclass in the "test" directory and various config files in the "test/conf.d" directory. There is another rspec file that tests the config_check function.

Why did I bother?

Having tried various config file solutions, I had ended up using yaml files, but i found checking them very difficult because they are not very friendly and very sensitive to spacing issues. In looking for yet another alternative, I came across the approach used by Unicorn (the backend web machine I now use for Rails apps). I liked the concept but thought it could be made more general, which resulted in Jeckyl.

The name Jeckyl is one of those silly acronyms that means nothing in particular: Jumpin' Ermin's Configurator for Kwick and easY Linux services

Bugs etc

Details of bugs can be found in {file:Bugs.rdoc}

Author and Contact

I am Robert Sharp and you can contact me on GitHub

Copyright and Licence

Copyright (c) 2011-2014 Robert Sharp.

See {file:LICENCE.rdoc LICENCE} for details of the licence under which Jeckyl is released.


This software is provided "as is" and without any express or implied warranties, including, without limitation, the implied warranties of merchantibility and fitness for a particular purpose.