Just, start using it!

A really quick introduction to Just command runner. What is it and how to use it?

A More Detailed Blog Post Suggestion

If you have time like ~10 minutes, I suggest you to read the "Just! Stop using Makefile" blog post written by The Orange One (Jake Howard). I first heard about Just from that blog post and I enjoyed reading it. You can find the post here: theorangeone.net/posts/just-stop-using-makefile/

My blog post is a quick introduction to Just. It's not a detailed guide, but it's enough to start using it.

What is Just?

Just is a cross-platform command runner, a tool that helps you to run commands defined in a file. It is really similar to Make, but it's focused on being a command runner rather than a build tool. For a command runner tool Just has improvements over Make, for example listing available recipes, passing arguments to recipes, and more.

What is a recipe? In Just, recipe is a command or command set that you want to run. Recipes are defined in a file called justfile (like the Makefile in Make). You can define multiple recipes in a justfile and run them by the name you set. justfile file naming is case-insensitive, personally I prefer to use Justfile to make it more visible.

Before going further, let me show you an example Justfile with 2 simple recipes:

Justfile

# Print "Hello World!"
hello:
    echo "Hello World!"

# Format swag comments, then genereate swagger files
swag:
    swag fmt -g cmd/restapi/main.go
    swag init --pd -d ./internal/controllers -g ../../cmd/restapi/main.go -o ./swagger

To execute a recipe, you can simply run $ just hello or $ just swag commands. Just like Make ;)

Install Just

Luckily, Just is available in most package managers. For example:

Fedora Ubuntu Homebrew

$ sudo dnf install just

$ sudo apt install just

$ brew install just

For other package managers check out Installation section on Just GitHub repo.

Use Just

To use Just, you need to create a Justfile in your project directory. You will define your recipes in this file. After creating the Justfile, you can run your recipes using $ just <name-of-your-recipe> command.

Justfile location

When you invoke just it looks for file justfile in the current directory and upwards, so you can invoke it from any subdirectory of your project.

- Just Manual

Hello World

Justfile

# Print "Hello World!"
hello:
    echo "Hello World!"

$ just hello
echo "Hello World!"
Hello World!

The comment line above the recipe is optional, if you add (which you should) it will be displayed next to the recipe names when you list the recipes.

Listing Recipes

You can list recipes defined in the Justfile by running $ just --list command.

Justfile

Justfile

# Start dev server
run:
    python3 -m src.app

# Run ruff check and format
ruff:
    ruff check src/ --fix
    ruff format src/

# Run type checking with mypy
mypy:
    mypy src/

# Running tests with pytest
test:
    pytest -v

$ just --list
Available recipes:
    mypy # Run type checking with mypy
    ruff # Run ruff check and format
    run  # Start dev server
    test # Running tests with pytest

Default Recipe

If you run just command without any arguments, it will run the first recipe in the Justfile. I prefer using the default recipe functionality to list available recipes.

Justfile

Justfile

# List available recipes
default:
    @just --list

# Start dev server
run:
    python3 -m src.app

# Run ruff check and format
ruff:
    ruff check src/ --fix
    ruff format src/

# Run type checking with mypy
mypy:
    mypy src/

# Running tests with pytest
test:
    pytest -v

$ just
Available recipes:
    default # List available recipes
    mypy    # Run type checking with mypy
    ruff    # Run ruff check and format
    run     # Start dev server
    test    # Running tests with pytest

Hide recipe from list

If you don't want a recipe to be listed in the recipes list, you can start the recipe name with an underscore _. For example, _default.

Recipe Parameters

You can add parameters to your recipes.

Justfile

Justfile

# Greet the user
greet username:
    echo "Hello, {{username}}!"

$ just greet Berk
echo "Hello, Berk!"
Hello, Berk!

---

There is a lot more features in Just. If you are interested, you should check out the Just Manual. It's really well documented and easy to understand.

Just GitHub Repo: github.com/casey/just
Just Manual: just.systems/man/en/

Cheat Sheet to explore Just features quickly: cheatography.com/linux-china/cheat-sheets/justfile/

Ohh, did I mention that Just is written in Rust?

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