Elixir make files

One of the common practices in Elixir is to use Makefiles and the Make compiling utility. Make was first released in 1977 and can be found installed on almost all *nix systems. Make uses a series of commands to compile projects. These commands are written in a Makefile. When Make runs, it checks to see if a Makefile exists in the current directory, and if so uses it.

Makefiles can be tricky if you don’t know what you’re doing, so in this post I’ll try an explain the base Makefile I use in my Elixir projects.

First thing to do is pick a location for our compiled code. I normally use the ebin directory. Lets set that to a variable.

EBIN_DIR=ebin

Variables in Make are set using capital letters. Next we need to write our compile task.

compile: ebin

ebin: lib/*.ex
  @ rm -f ebin/::*.beam
  @ echo Compiling ...
  @ mkdir -p $(EBIN_DIR)
  @ touch $(EBIN_DIR)
  elixirc lib/**/*.ex -o $(EBIN_DIR)
  @ echo

Tasks are written with the task name on the left, then a series of targets on the right. A target can be a group of files, or another task. If the target is a group of files, the task will only execute if the files have changed since it last ran.

In this case our compile task’s only target is the ebin task, though more can be added later. The ebin task watches all of the .ex files in the lib directory. If any of them have changed since the last time the task was run, it will remove all of the old compiled code, make sure the ebin directory exists, then use the elixirc command to compile the code and output the result to the ebin.

Using make we can also create a test task.

test: compile
  @ echo Running tests ...
  time elixir -pa ebin -r "test/**/*_test.exs"
  @ echo

Our test task makes sure the code is compiled, the uses the regular elixir command to load up the compiled code, then execute all of the tests.

Using Make, we can continue to add tasks to our program automating any procedure we seem to be doing over and over again.