Unifig is a pluggable system for loading external variables from one or more providers (e.g. ENV).

Version Test


If you are using a framework you should install the associated gem:

Framework Gem
Rails unifig-rails

If you want to use Unifig outside of a framework listed above you can manually add it to your project.

Add it to your Gemfile:

gem 'unifig', '~> 0.3.2'

Or install it manually:

$ gem install unifig --version '~> 0.3.2'

This project uses Semantic Versioning. Check out GitHub releases for a detailed list of changes.



Unifig loads a YAML configuration that instructs it on how to retrieve various external variables. These variable values come from providers. Unifig comes with a local provider which reads values straight from the configuration file. Additional providers may be installed.

The most minimal configuration would be:

  providers: local

  value: "world"

Given that configuration, Unifig will attach two new methods to the Unifig class. From in your code you can call Unifig.hello to get the value of the variable and Unifig.hello? to see if the value was retrieved (for optional values).

Unifig also allows you to override the overall configuration or the individual configuration by using environments. Here is an example where the production environment only pull from the env provider and in the test environment Unifig.hello will return dlrow:

  providers: [local, env]
        providers: env

  value: "world"
      value: "dlrow"

Variable Substitutions

Variables can be used in other variables with ${VAR}.

SERVICE_USERNAME: "${USER}_at_service"

Order of the variables does not matter but cyclical dependencies will throw an error.


Loading a configuration is handled through the Unifig::Init class. From Unifig::Init you can load the YAML as a string with .load or a file with .load_file.

All variables are assumed to be required (not nil or a blank string). Variables can be made optional by using the :optional setting. If there is a required variable without a value, Unifig will throw an error when loading.

Unifig::Init.load(<<~YAML, env: :production)
    providers: local

    value: github.com
        value: localhost
    optional: true
        value: 8080

> Unifig.host?
# true
> Unifig.host
# => "localhost"
> Unifig.port?
# true
> Unifig.port
# => 8080

If we replaced :development with :production inside the load call we'd get:

> Unifig.host?
# true
> Unifig.host
# => "github.com"
> Unifig.port?
# false
> Unifig.port
# => nil

You can load from a configuration file by using load_file.

Unifig::Init.load_file('unifig.yml', env: :production)

API Documentation

YAML Configuration

The configuration YAML must contain a config key. A list of one or more providers must be given. They are are checked in order to find the value for each variable. Variables are then listed by name.

The first level of configurations apply to all environments. These can be overridden by setting the envs key and a key with the name of then environment and then redefining any settings. This is the case for the overall configuration as well as any variable configurations.


Provider Gem
Local Built-in
ENV unifig-env


After loading the configuration you can use Unifig::Vars to check on what happened. It will return a list of Unifig::Vars with information such as which provider supplied the value.


If you want to contribute to Unifig, please read our contribution guidelines. A complete list of contributors is available on GitHub.


Unifig is licensed under the MIT License.