Create an Erlang application with Rebar3

This exercise runs outside the Zotonic workspace. Use Erlang/OTP 28 and Rebar3. Check erl and rebar3 version before starting.

Create and compile

In a directory for practice projects:

rebar3 new app garden_counter
cd garden_counter
rebar3 compile
rebar3 shell

The generated application contains src/garden_counter.app.src, src/garden_counter_app.erl, and src/garden_counter_sup.erl. Erlang source belongs in src; generated beam files are under _build/default/lib/garden_counter/ebin.

At the Erlang prompt:

application:ensure_all_started(garden_counter).
application:which_applications().

Starting an already running application is harmless. Check that garden_counter appears in the application list. The application callback starts the supervisor; the generated supervisor initially has no workers.

rebar3 shell starts a separate practice VM. You can use q(). to stop that VM. In a remote Zotonic shell, press Ctrl-C twice to leave; do not call q(). or halt(). there.

Add a test

Create test/garden_counter_tests.erl:

-module(garden_counter_tests).
-include_lib("eunit/include/eunit.hrl").

application_metadata_test() ->
    case application:load(garden_counter) of
        ok -> ok;
        {error, {already_loaded, garden_counter}} -> ok
    end,
    {ok, Description} = application:get_key(garden_counter, description),
    ?assert(is_list(Description)).

Run rebar3 eunit. Expect the test to pass. Continue with the supervised-worker recipe to add useful behaviour. Zotonic applications use Zotonic's own workspace build; do not run rebar3 new inside an existing site directory.