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Getting Started

First Steps

The best way to get going with Rebar is to use it to construct and build a simple Erlang application. First, let's create the directory for our application:

$ mkdir myapp; cd myapp

Now, download the rebar binary into our application. Note: if you have rebar available on your shell PATH, that will work equally well.

$ wget; chmod u+x rebar

Now, we'll use Rebar's templating system to create the skeleton of our application:

$ ./rebar create-app appid=myapp

The result of this command will be a single sub-directory, "src" which contains three files:

  • - The OTP application specification
  • myapp_app.erl - An implementation of the OTP Application behaviour
  • myapp_sup.erl - An implementation of an OTP Supervisor behaviour

We can now compile this application with rebar:

$ ./rebar compile

A new directory, "ebin/" will now exist and in it you will find the .beam files corresponding to the Erlang source files in the source directory. In addition, note the presence of ebin/ -- Rebar has dynamically generated a proper OTP application specification using the template in src/

To cleanup the directory after compiling simple do:

$ ./rebar clean


Rebar provides support for both eunit and common_test testing frameworks. In this example, we'll use eunit and write a simple unit test for our application.

In src/myapp_app.erl, after the -export() directive, add the following code:


In addition, at the end of the same file, add this code:


simple_test() ->
    ok = application:start(myapp),
    ?assertNot(undefined == whereis(myapp_sup)).


By wrapping the test code with that ifdef directive, we can be sure our test code won't be shipped as part of the compiled code in ebin. Let's run the unit test now:

$ ./rebar compile eunit

You should see output something like:

==> myapp (compile)
Compiled src/myapp_app.erl
==> myapp (eunit)
Compiled src/myapp_app.erl
  Test passed

Notice that Rebar compiled myapp_app.erl twice; the second compilation output to a special directory (.eunit) and includes debug information and other helpful testing flags.

If we want to check the coverage of our unit tests, we can easily do that by adding the following line to a rebar.config file:

{cover_enabled, true}.

Now re-run our tests:

$ ./rebar compile eunit
==> myapp (compile)
==> myapp (eunit)
  Test passed.
Cover analysis: /Users/dizzyd/tmp/myapp/.eunit/index.html

You can look in the .eunit/index.html file for details of the coverage analysis.