How to run erlang (rebar build) application - erlang

Question

I am new to Erlang world and currently can't figure out how to start my dummy erlang application. Probably, I am just missing something... So, I created an application with rebar (rebar create-app appid=dummys).
Currently I have
rebar.config
src/dummys.app.src
src/dummys_app.erl
src/dummys_sup.erl
I have found that in order to run an application during a development it is better to create an additional start method which should call application:start(module).
I added some basic logging to my start methods..
start() ->
error_logger:info_msg("Starting app(dev)..~n"),
application:start(dummys_app).
start(_StartType, _StartArgs) ->
error_logger:info_msg("Starting app..~n"),
dummys_sup:start_link().
If I try
erl -noshell -pa ebin -s application start dummys
erl -noshell -pa ebin -s application start dummys_app
there are no output..
If I try
erl -noshell -pa ebin -s dummys start
erl crashes with an error..
If I try
erl -noshell -pa ebin -s dummys_app start
it outputs just "Starting app(dev).." and that's all. But I also expect to see "Starting app.."
What I am missing or doing wrong??
=============
And another question: How to add a new module to my dummy application correctly? For example I have an additional module called "*dummys_cool*" which has a "start" method. How to tell my application to run that "dummys_cool#start" method?
Thank you!

Answer 1

For quick development, if you just want to ensure your appliction can start, start a shell, then start the application:
erl -pa ebin
1> dummys_app:start().
That will give you a clean indication of what is wrong and right without the shell bombing out after.
Since you're making an application to run, rather than just a library to share, you'll want to make a release. Rebar can get you most of the way there:
mkdir rel
cd rel
rebar create-node nodeid=dummysnode
After you've compiled your application, you can create a release:
rebar generate
This will build a portable release which includes all the required libraries and even the erlang runtime system. This is put by default in the rel/ directory; in your case rel/dummys.
Within that directory there will be a control script that you can use to start, stop, and attach to the application:
rel/dummys/bin/dummys start
rel/dummys/bin/dummys stop
rel/dummys/bin/dummys start
rel/dummys/bin/dummys attach

Answer 2

Have a look at your dummys.app.src file. The meaning of all the directives is explained in the 'app' manpage, but the one I suspect is missing here is mod, which indicates the name of your application callback module. So make sure that this line is present:
{mod, {dummys_app, []}}
The empty list in there will be passed as the StartArgs argument to dummys_app:start/2.
To make a new module start along with your application, add it to the supervision tree in dummys_sup:init. This function should look something like:
init(_) ->
{ok, {{one_for_one, 10, 10},
[{dummys_cool, {dummys_cool, start_link, []},
permanent, brutal_kill, worker, [dummys_cool]}]}.
This is described in the 'supervisor' manpage, but basically this means that on startup, this supervisor will start one child process. dummys_cool:start_link() will be called, and that function is expected to spawn a new process, link to it, and return its process id. If you need more processes, just add more child specifications to the list.

Answer 3

erl -noshell -pa ebin -s application start dummys
The code above will not work because application:start([dummys]) will be called.
You can take a reference of the Erlang documentation for details.
For your case,
erl -noshell -pa ebin -s dummys

Answer 4

I ran into this problem, and this was the first answer on Google.
If you are using rebar3, the standard configuration will have a shell command that compiles your project and opens a shell:
$ rebar3 shell
===> Analyzing applications...
===> Compiling myapp
Erlang/OTP 21 [erts-10.2.4] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1]
Eshell V10.2.4 (abort with ^G)
1> ===> Booted myapp