TTY::Config Gitter

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Define, read and write any Ruby app configurations with a penchant for terminal clients.

TTY::Config provides app configuration component for TTY toolkit.


  • Read & write configurations in YAML, JSON, TOML formats
  • Simple interface for setting and fetching values for deeply nested keys
  • Merging of configuration options from other hashes


Add this line to your application's Gemfile:

gem 'tty-config'

And then execute:

$ bundle

Or install it yourself as:

$ gem install tty-config


1. Usage

Initialize the configuration and provide the name:

config =
config.filename = 'investments'

then configure values for different nested keys with set and append:

config.set(:settings, :base, value: 'USD')
config.set(:settings, :color, value: true)
config.set(:coins, value: ['BTC'])

config.append('ETH', 'TRX', 'DASH', to: :coins)

get any value by using fetch:

config.fetch(:settings, :base)
# => 'USD'

# => ['BTC', 'ETH', 'TRX', 'DASH']

and write configration out to investments.yml:

# =>
# ---
# settings:
#   base: USD
#   color: true
# coins:
#  - BTC
#  - ETH
#  - TRX
#  - DASH

and then to read an investments.yml file, you need to provide the locations to search in:

config.append_path Dir.pwd
config.append_path Dir.home

Finally, read in configuration back again:

1.1 app

An example of an application configuration:

class App
  attr_reader :config

  def initialize
    @config =
    @config.filename = 'investments'
    @config.extname = '.toml'
    @config.append_path Dir.pwd
    @config.append_path Dir.home

  def self.config
    @config ||=

2. Interface

2.1 set

To set configuration setting use set method. It accepts any number of keys and value by either using :value keyword argument or passing a block:

config.set(:base, value: 'USD')
config.set(:base) { 'USD' }

The block version of specifying a value will mean that the value is evaluated every time its being read.

You can also specify deeply nested configuration settings by passing sequence of keys:

config.set :settings, :base, value: 'USD'

is equivalent to:

config.set 'settings.base', value: 'USD'

Internally all configuration settings are stored as string keys for ease of working with configuration files and command line application's inputs.

2.2 set_if_empty

To set a configuration setting only if it hasn't been set before use set_if_empty:

config.set_if_empty :base, value: 'USD'

Similar to set it allows you to specify arbitrary sequence of keys followed by a key value or block:

config.set_if_empty :settings, :base, value: 'USD'

2.3 fetch

To get a configuration setting use fetch, which can accept default value either with a :default keyword or a block that will be lazy evaluated:

config.fetch(:base, default: 'USD')
config.fetch(:base) { 'USD' }

Similar to set operation, fetch allows you to retrieve deeply nested values:

config.fetch(:settings, :base) # => USD

is equivalent to:


fetch has indifferent access so you can mix string and symbol keys, all the following examples retrieve the value:

config.fetch(:settings, :base)
config.fetch('settings', 'base')
config.fetch(:settings', 'base')
config.fetch('settings', :base)

2.4 merge

To merge in other configuration settings as hash use merge:

config.set(:a, :b, value: 1)
config.set(:a, :c, value: 2)

config.merge({'a' => {'c' => 3, 'd' => 4}})

config.fetch(:a, :c) # => 3
config.fetch(:a, :d) # => 4

Internally all configuration settings are stored as string keys for ease of working with file values and command line applications inputs.

2.5 coerce

You can initialize configuration based on a hash, with all the keys converted to symbols:

hash = {"settings" => {"base" => "USD", "exchange" => "CCCAGG"}}
config = TTY::Config.coerce(hash)
# =>
# {settings: {base: "USD", exchange: "CCCAGG"}}

2.6 append

To append arbitrary number of values to a value under a given key use append:

config.set(:coins) { ["BTC"] }

config.append("ETH", "TRX", to: :coins)
# =>
# {coins: ["BTC", "ETH", "TRX"]}

You can also append values to deeply nested keys:

config.set(:settings, :bases, value: ["USD"])

config.append("EUR", "GBP", to: [:settings, :bases])
# =>
# {settings: {bases: ["USD", "EUR", "GBP"]}}

2.7 remove

Use remove to remove a set of values from a key.

config.set(:coins, value: ["BTC", "TRX", "ETH", "DASH"])

config.remove("TRX", "DASH", from: :coins)
# =>
# ["BTC", "ETH"]

If the key is nested the :from accepts an array:

config.set(:holdings, :coins, value: ["BTC", "TRX", "ETH", "DASH"])

config.remove("TRX", "DASH", from: [:holdings, :coins])
# =>
# ["BTC", "ETH"]

2.8 delete

To completely delete a value and corresponding key use delete:

config.set(:base, "USD")
# =>
# "USD"

You can also delete deeply nested keys and their values:

config.set(:settings, :base, "USD")
config.delete(:settings, :base)
# =>
# "USD"

2.9 validate

To ensure consistency of the data, you can validate values being set at arbitrarily deep keys using validate method, that takes an arbitrarily nested key as its argument and a validation block.

config.validate(:settings, :base) do |key, value|
  if value.length != 3
    raise TTY::Config::ValidationError, "Currency code needs to be 3 chars long."

You can assign multiple validations for a given key and each of them will be run in the order they were registered when checking a value.

When setting value all the validaitons will be run:

config.set(:settings, :base, value: 'PL')
# raises TTY::Config::ValidationError, 'Currency code needs to be 3 chars long.'

If the value s provided as a proc or a block then the validation will be delayed until the value is actually read:

config.set(:settings, :base) { 'PL' }
config.fetch(:settings, :base)
# raises TTY::Config::ValidationError, 'Currency code needs to be 3 chars long.'

2.10 filename=

By default, TTY::Config searches for config named configuration file. To change this use filename= method without the extension name:

config.filename = 'investments'

Then any supported extensions will be search for such as .yml, .json and .toml.

2.11 extname=

By default '.yml' extension is used to write configuration out to a file but you can change that with extname=:

config.extname = '.toml'

2.12 append_path

You need to tell the TTY::Config where to search for configuration files. To search multiple paths for a configuration file use append_path or prepend_path methods.

For example, if you want to search through /etc directory first, then user home directory and then current directory do:

config.append_path("/etc/")   # look in /etc directory
config.append_path(Dir.home)  # look in user's home directory
config.append_path(Dir.pwd)   # look in current working directory

None of these paths are required, but you should provide at least one path if you wish to read configuration file.

2.13 prepend_path

The prepend_path allows you to add configuration search paths that should be searched first.

config.append_path(Dir.pwd)   # look in current working directory second
config.prepend_path(Dir.home) # look in user's home directory first

2.14 read

There are two ways for reading configuration files and both use the read method.

First one, searches through provided locations to find configuration file and read it. Therefore, you need to specify at least one search path that contains the configuration file.

config.append_path(Dir.pwd)       # look in current working directory
config.filename = 'investments'   # file to search for

Find and read the configuration file:

However, you can also specify directly the file to read without setting up any search paths or filenames:'./investments.toml')

2.15 write

By default TTY::Config, persists configuration file in the current working directory with a config.yml name. However, you can change that by specifying the filename and extension type:

config.filename = 'investments'
config.extname = '.toml'

To write current configuration to a file, you can either specified direct location path and filename:


Or, specify location paths to be searched for already existing configuration to overwrite:

config.append_path(Dir.pwd)  # search current working directory


To create configuration file regardless whether it exists or not, use :force flag:

config.write(force: true)                        # overwrite any found config file
config.write('./investments.toml', force: true)  # overwrite specific config file

2.16 persisted?

To check if a configuration file exists within the configured search paths use persisted? method:

config.persisted? # => true


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at[USERNAME]/tty-config. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the Tty::Config project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.

Copyright (c) 2018 Piotr Murach. See LICENSE for further details.