Mix and Dependencies

mix new my_app              # basic project
mix new my_app --sup        # project with supervision tree
mix new my_app --umbrella   # umbrella project (multiple apps)

my_app/
├── mix.exs            # Project definition, deps, config
├── mix.lock            # Locked dependency versions (auto-generated)
├── config/
│   └── config.exs      # Application config
│   └── dev.exs         # Dev environment config
│   └── test.exs        # Test environment config
│   └── prod.exs        # Production config (often secrets)
│   └── releases.exs    # Release config (optional)
├── lib/
│   └── my_app.ex        # Main module
│   └── my_app/          # Additional modules
├── test/
│   ├── test_helper.exs
│   └── my_app_test.exs
├── .formatter.exs       # Code formatter config
└── .gitignore

defmodule MyApp.MixProject do
  use Mix.Project

  def project do
    [
      app: :my_app,
      version: "0.1.0",
      elixir: "~> 1.16",
      start_permanent: Mix.env() == :prod,
      deps: deps(),
      aliases: aliases()
    ]
  end

  def application do
    [
      extra_applications: [:logger],
      mod: {MyApp.Application, []}
    ]
  end

  defp deps do
    [
      {:phoenix, "~> 1.7"},
      {:ecto_sql, "~> 3.10"},
      {:jason, "~> 1.4"},
      {:ex_machina, "~> 2.7", only: :test}
    ]
  end

  defp aliases do
    [
      setup: ["deps.get", "ecto.setup"],
      "ecto.setup": ["ecto.create", "ecto.migrate"],
      "ecto.reset": ["ecto.drop", "ecto.setup"],
      test: ["ecto.create --quiet", "ecto.migrate --quiet", "test"]
    ]
  end
end

mix deps.get              # Fetch deps from mix.exs
mix deps.update phoenix   # Update a specific dep
mix deps.update --all     # Update all deps
mix deps.clean phoenix    # Clean a dep (forces rebuild)
mix deps.clean --all      # Clean all deps
mix deps.tree             # Show dependency tree
mix deps.unlock --all     # Unlock all deps (removes mix.lock entries)

import Config

config :my_app,
  greeting: "Hello"

config :my_app, MyApp.Repo,
  database: "my_app_dev",
  hostname: "localhost"

config :logger, :console,
  format: "$time $metadata[$level] $message\n",
  metadata: [:request_id]

import_config "#{config_env()}.exs"

# At compile time (in mix.exs or config)
greeting = Application.get_env(:my_app, :greeting)

# At runtime (preferred for releases)
defmodule MyApp.Config do
  def greeting, do: Application.fetch_env!(:my_app, :greeting)
end

import Config

config :my_app, MyApp.Repo,
  url: System.get_env("DATABASE_URL") || "ecto://localhost/my_app_dev",
  pool_size: String.to_integer(System.get_env("POOL_SIZE") || "10")

config :my_app, MyAppWeb.Endpoint,
  url: [host: System.get_env("PHX_HOST") || "localhost", port: 443],
  secret_key_base: System.fetch_env!("SECRET_KEY_BASE")

iex                        # Start REPL
iex -S mix                 # Start REPL with project loaded
iex -S mix phx.server      # Start Phoenix server with REPL