A rebar plugin

$ rebar3 compile

Add the plugin to your rebar config:

{plugins, [
    {myplug, {git, "https://host/user/myplug.git", {tag, "0.1.0"}}}
]}.

Then just call your plugin directly in an existing application:

$ rebar3 myplug
===> Fetching myplug
===> Compiling myplug
<Plugin Output>