Erlang: programmatically get application version

Question

I have an OTP application. The version of this application is found in two places: the src/application_name.src file (standard with OTP applications), and in my rebar.config.

Is there an "official" way for an application to get it's own version, or does this need to be hacked via sed/grep etc? I want to have an "info" endpoint in my application that prints it's own version. Of course I can always do something like grep the version out of my rebar.config, but it seems hacky.

Answer 1

According to the Erlang documentation you can use API of application module.

Example:

Erlang/OTP 19 [erts-8.2.2] [source-1ca84a4] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]

Eshell V8.2.2  (abort with ^G)
1> application:loaded_applications().
[{stdlib,"ERTS  CXC 138 10","3.2"},
{kernel,"ERTS  CXC 138 10","5.1.1"}]

2> GetVer = 
fun(App) ->
    case lists:keyfind(App, 1, application:loaded_applications()) of
        {_, _, Ver} ->
            Ver;
        false ->
            not_found
    end
end.
#Fun<erl_eval.6.52032458>

3> GetVer(stdlib).
"3.2"

4> GetVer(eunit). 
not_found

5> application:load(eunit).
ok

6> GetVer(eunit).          
"2.3.2"

7>

Answer 2

If it is properly packaged as an application, you can get it using application:which_applications(). I have some sample code, but basically you'd do something like this:

vsn() -> vsn(your_application_atom_name).

vsn(Application) -> vsn(Application, application:which_applications()).
vsn(_Application, []) -> undefined;
vsn(Application, [{Application,_,Vsn}|_]) -> Vsn;
vsn(Application, [_|Rest]) -> vsn(Application, Rest).

The downside is that you do have to hardcode the name of your application (as an atom). I never found a way around this, but you might be able to cook something up.