Mix.env/0 equivalent in production env?

Question

Mix.env/0 works correctly in mix phoenix.server, but it fails to call in a production environment which is built with exrm. It makes sense because mix isn't included in the release build, but is there any equivalent of Mix.env/0?

(UndefinedFunctionError) undefined function Mix.env/0 (module Mix is not available)

I'm using Mix.env/0 like this in some code:

if Mix.env == :dev do
  # xxxxxx
else
  # xxxxxx
end

Answer 1

You can simply define a config value for the environment:

config/prod.exs

config :my_app, :environment, :prod 

config/dev.exs

config :my_app, :environment, :dev 

You can then check that value using Application.get_env/3

if Application.get_env(:my_app, :environment) == :dev do 

However, I would recommend giving this more context. Let's say you want to conditionally apply an authentication plug in production, you could set the config to:

config :my_app, MyApp.Authentication,   active: true  if Application.get_env(:my_app, MyApp.Authentication) |> Keyword.get(:active) do   #add the plug 

This way, your conditions are feature based instead of environment based. You can turn them on and off regardless of environment.

Answer 2

You can evoque Mix.env/0 as a module constant at compile time like this :

@env Mix.env
#...
if @env == :dev do
#...

Works like a charm with releases.