Mix: A Beginner’s Guide to Elixir’s Build Tool and Dependency Manage

Introduction

Mix is Elixir’s default build tool, designed to automate common tasks like project creation, compilation, testing, and dependency management. While similar to tools like dotnet CLI, Mix offers deeper extensibility and is tightly integrated with Elixir’s ecosystem.

Core Features

1. Creating a Project

Generate a new Elixir project with a single command:

mix new friends  

This creates a structured project with a mix.exs file at its core.

1. The mix.exs File

This file defines project settings, dependencies, and tasks. Here’s a minimal example:

defmodule Friends.MixProject do  
  use Mix.Project  

  def project do  
    [  
      app: :friends,  
      version: "0.1.0",  
      elixir: "~> 1.18",  
      start_permanent: Mix.env() == :prod,  
      deps: deps()  
    ]  
  end  

  def application do  
    [extra_applications: [:logger]]  
  end  

  defp deps do  
    [] # Dependencies go here  
  end
end 

Dependency Management

Adding Dependencies

Edit the deps function in mix.exs:

defp deps do  
  [  
    {:ecto_sql, "~> 3.0"},  
    {:postgrex, ">= 0.0.0"}  
  ]  
end  

Note: Unlike npm or cargo, Mix lacks a mix deps.add command—edit mix.exs manually.

Restoring Dependencies

mix deps.get      # Fetches dependencies
mix deps.compile  # Compiles them

Updating Dependencies

Update a single package:

mix deps.update ecto_sql  

Update all packages:

mix deps.update --all

Mix uses a mix.lock file to ensure consistent versions across environments.

Common Workflows

Compiling the Project

mix compile  

Running Tests

mix test

Extending Mix

Aliases

Mix aliases are custom shortcuts defined in your mix.exs file to simplify or combine repetitive tasks. They allow you to:

• Chain multiple Mix commands into one.
• Create project-specific workflows.
• Simplify complex build/test/deploy processes.

def project do  
  [  
    ...,  
    aliases: aliases()  
  ]  
end  

defp aliases do  
  [  
    build_test: ["compile", "test"],  
    "build:test": ["compile", "test"]  
  ]  
end  

Run with:

mix build_test  

Custom Tasks

Create reusable tasks (e.g., lib/mix/tasks/hello.ex):

defmodule Mix.Tasks.Hello do  
  @moduledoc "Prints a greeting: `mix help hello`"  
  use Mix.Task  

  @shortdoc "Prints 'hello' to the console"  
  def run(_args) do  
    IO.puts("hello")  
  end  
end  

Run with:

mix hello

Why Mix Shines

• Extensible: Frameworks like Phoenix and Ecto add their own tasks (e.g., mix ecto.gen.repo).
• Batteries Included: Built-in tasks for testing, compilation, and dependency management.
• Community-Driven: Most Elixir libraries integrate seamlessly with Mix.

Conclusion

Mix is the backbone of Elixir development. Its simplicity for common tasks and flexibility for customization make it indispensable.

Next Steps:

• Explore Mix’s official documentation.
• Learn advanced workflows with Elixir School.