# Skogsrå
[](https://travis-ci.org/gmtprime/skogsra) [](https://hex.pm/packages/skogsra) [](https://hex.pm/packages/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.
* Variable defaults.
* Automatic documentation generation for variables.
* Runtime reloading.
* Setting variable's values at runtime.
* Fast cached values access by using `:persistent_term` as temporal storage.
## Small Example
You would create a settings module e.g:
```elixir
defmodule MyApp.Settings do
use Skogsra
@envdoc "My hostname"
app_env :my_hostname, :myapp, :hostname,
default: "localhost"
end
```
Calling `MyApp.Settings.my_hostname()` will retrieve the value for the
hostname in the following order:
1. From the OS environment variable `$MYAPP_HOSTNAME`.
2. From the configuration file e.g:
```
config :myapp,
hostname: "my.custom.host"
```
3. From the default value if it exists (In this case, it would return
`"localhost"`).
## Handling different environments
If it's necessary to keep several environments, it's possible to use a
`namespace` e.g:
Calling `MyApp.Settings.my_hostname(Test)` will retrieve the value for the
hostname in the following order:
1. From the OS environment variable `$TEST_MYAPP_HOSTNAME`.
2. From the configuration file e.g:
```
config :myapp, Test,
hostname: "my.custom.test.host"
```
3. From the OS environment variable `$MYAPP_HOSTNAME`.
4. From the configuraton file e.g:
```
config :myapp,
hostname: "my.custom.host"
```
5. From the default value if it exists.
## Required variables
It is possible to set a environment variable as required with the `required`
option e.g:
```elixir
defmodule MyApp.Settings do
use Skogsra
@envdoc "My port"
app_env :my_port, :myapp, :port,
required: true
end
```
If the variable `$MYAPP_PORT` is undefined and the configuration is missing,
calling to `MyApp.Settings.my_port()` will return an error tuple. Calling
`$MyApp.Settings.my_port!()` (with the bang) will raise a runtime
exception.
## Automatic casting
If the default value is set, the OS environment variable value will be casted
as the same type of the default value. Otherwise, it is possible to set the
type for the variable with the option `type`. The available types are
`:binary` (default), `:integer`, `:float`, `:boolean` and `:atom`.
Additionally, you can create a function to cast the value and specify it as
`{module_name, function_name}` e.g:
```elixir
defmodule MyApp.Settings do
use Skogsra
@envdoc "My channels"
app_env :my_channels, :myapp, :channels,
type: {__MODULE__, channels},
required: true
def channels(value), do: String.split(value, ", ")
end
```
If `$MYAPP_CHANNELS`'s value is `"ch0, ch1, ch2"` then the casted value
will be `["ch0", "ch1", "ch2"]`.
## Setting and reloading variables
It's possible to set a value for the variable at runtime with e.g.
`MyApp.Settings.put_my_hostname("my.other.hostname")`.
Also, for debugging purposes is possible to reload variables at runtime with
e.g. `MyApp.Settings.reload_my_hostname()`.
## Using with _Hab_
[_Hab_](https://github.com/alexdesousa/hab) is an
[Oh My ZSH](https://github.com/robbyrussell/oh-my-zsh) plugin for loading OS
environment variables automatically.
By default, _Hab_ will try to load `.envrc` file, but it's possible to have
several of those files for different purposes e.g:
- `.envrc.prod` for production OS variables.
- `.envrc.test` for testing OS variables.
- `.envrc` for development variables.
_Hab_ will load the development variables by default, but it can load the
other files using the command `load_hab <extension>` e.g. loading
`.envrc.prod` would be as follows:
```bash
~/my_project $ load_hab prod
[SUCCESS] Loaded hab [/home/user/my_project/.envrc.prod]
```
## Installation
The package can be installed by adding `skogsra` to your list of dependencies
in `mix.exs`.
- For Elixir < 1.7 and Erlang < 21:
```elixir
def deps do
[{:skogsra, "~> 1.0.4"}]
end
```
- For Elixir < 1.8 and ≥ 1.7 and Erlang < 22 and ≥ 21
```elixir
def deps do
[{:skogsra, "~> 1.2"}]
end
```
- For Elixir ≥ 1.8 and Erlang ≥ 22
```elixir
def deps do
[{:skogsra, "~> 1.3"}]
end
```
## Author
Alexander de Sousa.
## License
_Skogsrå_ is released under the MIT License. See the LICENSE file for further
details.
