[erlang-questions] Debugging apps with dependencies

Bob Ippolito <>
Mon Apr 30 20:39:25 CEST 2012

On Mon, Apr 30, 2012 at 11:05 AM, Josh Black <> wrote:

> Hi, erlang beginner here.
> I have a question about the best way to debug apps which include
> dependencies.
> I'm working on an app, and so far, I've been testing it by using rebar to
> generate a release, then starting a console for the release and going from
> there.  The problem comes when I want to use something like dbg or appmon
> to debug errors or inspect the state of my app.  When I try to do, e.g.
> appmon:start() from the console for my release, it tells me "undefined
> function appmon:start/0".  I'm guessing this is because I didn't explicitly
> specify appmon in my release configuration?
> Alternatively, I created a start.sh shell script with contents like this:
> erl -pa apps/*/ebin -pa deps/*/ebin -eval 'application:start(dependency1),
> application:start(dependency2), application:start(myapp).'
> This lets me start appmon and whatever else I want when I run into errors,
> but feels pretty messy and wrong.
> I feel like I'm missing something really obvious here.  What's the correct
> way to do this?

I haven't discovered a great workflow for developing with releases either,
but you can start dependencies in a slightly cleaner way by looking at the
app file:

This would go in some module with the same name as the application, and you
would call it with "erl ... -s modname"


start() -> start(?MODULE).

start(App) ->
    {ok, Deps} = application:get_key(App, applications),
    lists:foreach(fun start_app/1, Deps),

start_app(App) ->
    case application:start(App) of
        {error, {already_started, _}} -> ok;
        ok -> ok
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