Given a file path, this function expands it to an absolute path, while also expanding any environment variable references in the path.

Examples

iex> var = String.replace("Elixir.Mix.Releases.Config.Provider", ".", "_")
...> System.put_env(var, "hello")
...> {:ok, "var/hello/test"} = Elixir.Mix.Releases.Config.Provider.expand_path("var/${" <> var <> "}/test")

iex> {:ok, "/" <> _} = Elixir.Mix.Releases.Config.Provider.expand_path("~/")

iex> {:error, :unclosed_var_expansion} = Elixir.Mix.Releases.Config.Provider.expand_path("var/${FOO/test")

Called when the provider is being asked to supply a value for the given key

Keys supplied to providers are a list of atoms which represent the path of the configuration key, beginning with the application name:

NOTE: This is currently unused, but provides an API for fetching config values from specific providers, which may come in handy down the road. A default implementation is provided for you, which fetches values from the application environment.

Examples

> MyProvider.get([:myapp, :server, :port])
{:ok, 8080}

> MyProvider.get([:maypp, :invalid, :key])
nil

Called when the provider is initialized.

This function is called early during the boot sequence, after all applications are loaded, but only :kernel, :stdlib, :compiler, and :elixir are started. This means that you cannot expect supervisors and processes to be running. You may need to start them manually, or start entire applications manually, but it is critical that you stop them before returning from init/1, or the boot sequence will fail post-configuration.

The arguments given to init/1 are the same as given in the config_providers setting in your release configuration file.

NOTE: It is recommended that you use init/1 to load configuration and then persist it into the application environment, e.g. with Application.put_env/3. This ensures that applications need not be aware of your specific configuration provider.