Skogsra

The Skogsrå was a mythical creature of the forest that appears in the form of a small, beautiful woman with a seemingly friendly temperament. However, those who are enticed into following her into the forest are never seen again.

This library attempts to improve the use of OS environment variables for application configuration:

Automatic type casting of values.
Options documentation.
Variables defaults.

Small Example

You would create a settings module and define the e.g:

defmodule MyApp.Settings do
  use Skogsra

  system_env :some_service_port,
    default: 4000

  app_env :some_service_hostname, :my_app, :hostname,
    domain: MyApp.Domain,
    default: "localhost"
end

and you would use it in a module as follows:

defmodule MyApp.SomeModule do
  alias MyApp.Setting

  (...)

  def connect do
    hostname = Settings.some_service_hostname()
    port = Settings.some_service_port()

    SomeService.connect(hostname, port)
  end

  (...)
end

Example Explanation

The module MyApp.Settings will have two functions e.g:

some_service_port/0: Returns the port as an integer. Calling this function is roughly equivalent to the following code (without the automatic type casting):
```
System.get_env("SOME_SERVICE_PORT") || 4000
```

some_service_hostname/0: Returns the hostname as a binary. Calling this function is roughly equivalent to the following code (without the automatic type casting):

case System.get_env("SOME_SERVICE_HOSTNAME") do
  nil ->
    :my_app
    |> Application.get_env(MyApp.Domain, [])
    |> Keyword.get(:hostname, "localhost")
  value ->
    value
end

Things to note:

The functions have the same name as the OS environment variable, but in lower case.
The functions infer the type from the default value. If no default value is provided, it will be casted as binary by default.
Both functions try to retrieve and cast the value of an OS environment variable, but the one declared with app_env searches for :my_app configuration if the OS environment variable is empty:
```
config :my_app, MyApp.Domain,
  hostname: "some_hostname"
```

If the default value is not present, Skogsra cannot infer the type, unless the type is set with the option type. The possible values for type are :integer, :float, :boolean, :atom and :binary.

Recommended Usage

The recommended way of using this project is to define a .env file in the root of your project with the variables that you want to define e.g:

export SOME_SERVICE_PORT=1234

and then when sourceing the file right before you execute your application. In bash (or zsh) would be like this:

$ source .env

The previous step can be automated by adding the following code to your ~/.bashrc (or ~/.zshrc):

#################
# BEGIN: Auto env

export LAST_ENV=

function auto_env_on_chpwd() {
  env_type="$1"
  env_file="$PWD/.env"
  if [ -n "$env_type" ]
  then
    env_file="$PWD/.env.$env_type"
    if [ ! -r "$env_file" ]
    then
      echo -e "\e[33mFile $env_file does not exist.\e[0m"
      env_file="$PWD/.env"
    fi
  fi

  if [ -n "$LAST_ENV" ] && [ -r "$LAST_ENV" ]
  then
    UNSET=$(cat $LAST_ENV | sed -e 's/^export \([0-9a-zA-Z\_]*\)=.*$/unset \1/')
    source <(echo "$UNSET")
    echo -e "\e[33mUnloaded ENV VARS defined in \"$LAST_ENV\"\e[0m"
    export LAST_ENV=
  fi

  if [ -r "$env_file" ]
  then
    export LAST_ENV="$env_file"
    source $LAST_ENV
    echo -e "\e[32mLoaded \"$LAST_ENV\"\e[0m"
  fi
}

chpwd_functions=(${chpwd_functions[@]} "auto_env_on_chpwd")

if [ -n "$TMUX" ]
then
  auto_env_on_chpwd
fi

alias change_to='function _change_to() {auto_env_on_chpwd $1}; _change_to'

# END: Auto env
###############

The previous code will attempt to source any .env file every time you change directory e.g:

/home/alex $ cd my_app
Loaded "/home/alex/my_app/.env"

/home/alex/my_app $ echo "$SOME_SERVICE_PORT"
1234

Additionally, the command change_to <ENV> is included. To keep your prod, dev and test environment variables separated, just create a .env.${MIX_ENV} in the root directory of your project. And when you want to use the variables set in one of those files, just run the following:

$ change_to dev # Will use `.env.dev` instead of `.env`

Installation

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

def deps do
  [{:skogsra, "~> 0.2"}]
end

Author

Alexander de Sousa.

License

Skogsra is released under the MIT License. See the LICENSE file for further details.