Check environment variables accoring to a .env.example file
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Env Lint

Gem Version Build Status

Check configuration of 12 factor apps according to to a .env.example file.

  • Avoid spelling errors in variable names in your code or on the command line
  • Ensure all relevant environment variables are described in the .env.example file.
  • Ensure all required environment variables are configured before deploying a new version of an app
  • Ease setting up a new development machine
  • Plays well with dotenv

If you'd rather read some prose, there's also a blog post explaining why we got started with env_lint.


Used in production. Following semantic versioning. Capistrano tasks only tested with recap capistrano tasks.


Add this line to your application's Gemfile:

gem 'env_lint'


Define a .env.example file:

# Explain each variable in comments like this one

# Comments are also recognized if they span multiple
# lines

# Optional variables
# OPTIONAL_VAR="set me if you like"

Rake Task

Require it in your Rakefile:

require 'env_lint/tasks'

Now you can check your environment:

$ rake env:lint
=> Complains if non optional variables are missing

If special steps are needed to setup your env, you can define a env:load task. For example to integrate with Dotenv:

require 'env_lint/tasks'
require 'dotenv'

namespace :env do
  task :load do

Capistrano Task

Require it in your Capfile:

require 'env_lint/capistrano'

Now you can check your servers:

$ cap env:lint
=> Complains if non optional variables are missing

You might want to lint the environment automatically before each deploy:

before 'deploy', 'env:lint'

By default, env_lint tries to run export as your recap application user. The probe command can be configured:

set(:env_probe_command, "su - deploy -c 'export'")

Lint variable names before setting them:

before 'env:set', 'env:lint_args'

$ cap env:set APP_NAME=myapp
=> Complains if APP_NAME is not defined

Lint at Runtime

Access ENV through a LintedEnv:

require 'env_lint'

class MyApp
  LINTED_ENV = EnvLint::LintedEnv.from_file('.env.example')

  def self.env

Accessing env variables:

# Ensures APP_NAME is defined in .env.example
MyApp.env.fetch(:app_name, 'App name')

# Ensures APP_NAME is non optional in .env.example


  • ENV_BANG - Offers a ruby DSL. Comes with type conversion features. Does not include tasks to check environment variables without running the app.


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request