I am following a phoenix book which says:
Be careful. The ecto.migrate task will migrate the database for your current environment. So far, we’ve been running the dev environment. To change the environment, you’d set the MIX_ENV operating-system environment variable.
But I dont know which is mi current environment, I print echo MIX_ENV variable and it's empty, how can I knowwhich environment I am in and/or change from environments?