EnvConfig

EnvConfig is a library that makes it easier to write runtime.exs files that take in parameters from the environment.

The idea is that EnvConfig allows you to define which environment variables an application needs, what their type is expected to be, and whether they are optional for the application to start.

The api ensures that the values are read from the environment and are cast into their proper Elixir types.

Before

import Config

if config_env() == :prod do
  secret_key_base =
    System.get_env("SECRET_KEY_BASE") ||
      raise """
      environment variable SECRET_KEY_BASE is missing.
      You can generate one by calling: mix phx.gen.secret
      """

  if System.get_env("PHX_SERVER") do
    config :my_app, MyAppWeb.Endpoint, server: true
  end
end

After

import Config
require EnvConfig.Macros
import EnvConfig.Macros

if config_env() == :prod do
  secret_key_base = required("SECRET_KEY_BASE", :string, min_length: 64)

  phx_server = optional("PHX_SERVER", :boolean, false)
  config :my_app, MyAppWeb.Endpoint, server: phx_server
end

If the environment variable is not defined, you will see the same error.

** (RuntimeError) Environment variable SECRET_KEY_BASE is not set
    /Users/christophe/Documents/Code/loomy/data-api/config/runtime.exs:5: (file)
    (stdlib 6.2) erl_eval.erl:919: :erl_eval.do_apply/7
    (stdlib 6.2) erl_eval.erl:663: :erl_eval.expr/6
    (stdlib 6.2) erl_eval.erl:271: :erl_eval.exprs/6
    (elixir 1.18.1) lib/code.ex:572: Code.validated_eval_string/3

Or, when the type or constraints are not met, an error explaining whats wrong.

** (RuntimeError) Environment variable SECRET_KEY_BASE does not meet constraints. string is shorter than 64 characters
    /Users/christophe/Documents/Code/loomy/data-api/config/runtime.exs:5: (file)
    (stdlib 6.2) erl_eval.erl:919: :erl_eval.do_apply/7
    (stdlib 6.2) erl_eval.erl:663: :erl_eval.expr/6
    (stdlib 6.2) erl_eval.erl:271: :erl_eval.exprs/6
    (elixir 1.18.1) lib/code.ex:572: Code.validated_eval_string/3

Installation

The package can be installed by adding env_config to your list of dependencies in mix.exs:

The package will be published on hex as soon as it is stable enough.

def deps do
  [
    {:env_config, git: "https://github.com/m1dnight/env_config"}
  ]
end

Types

EnvConfig supports basic types out of the box, and lists of these types.

Type	Values	Elixir Type
:boolean	true, TRUE, 1, false, FALSE, 0	boolean()
:string	any value	String.t()
:atom	any value	atom()
:charlist	any value	charlist()
:integer	any integral value that's parsable as an integer using &Integer.parse/1	integer()
:float	any value that's parsable as a float using &Float.parse/1	float()
{:list, type}	a comma-separated list of values for any given type in the above table.	[type]
{:enum, [binary]}	any value that is a member of the values given in the list of the enum type.	String.t()

Constraints

Constraint	Applicaple types	Description
{:length, n}	{:list, type}	Exact length the list should be.
{:min_length n}	{:list, type}	Minimal length the list should be.
{:max_length, n}	{:list, type}	Maximal length the list should be.
{:min, n}	:integer	Minimal value for the integer.
{:max, n}	:integer	Maximum value for the integer.
{:allow_empty?, boolean()}	:string	Is the env value allowed to be empty? Strings are trimmed before getting length.
{:max_length, n}	:string	Maximum length of the string. Strings are trimmed before getting length.
{:min_length, n}	:string	Minimal length of the string. Strings are trimmed before getting length.