Just

What is Just?

Just is a command runner — similar to make, but designed specifically for running project tasks rather than building software. It uses a simple syntax, supports arguments, and works across platforms.

Unlike make, Just does not track file dependencies or timestamps. It simply runs the commands you define. This makes it ideal for tasks like deploying configs, running scripts, or orchestrating multi-step workflows.

Prerequisites

None — Just works with any shell and operating system.

Installation

brew install just

# Debian / Ubuntu (via prebuilt binary)
curl --proto '=https' --tlsv1.2 -sSf https://just.systems/install.sh | bash -s -- --to ~/bin

# Or via package manager (if available)
sudo apt install just

Your First Justfile

Create a file named Justfile (or justfile) at the root of your project:

# List available recipes (runs when you type `just` with no arguments)
default:
    @just --list

# Run a simple task
greet name="world":
    echo "Hello, {{name}}!"

Run it:

# List recipes
just

# Run a recipe
just greet

# Pass an argument
just greet "developer"

Core Concepts

Recipes

Recipes are the tasks you define. Each recipe has a name, optional parameters, and one or more shell commands:

# Recipe with no arguments
build:
    echo "Building..."

# Recipe with a required argument
deploy target:
    echo "Deploying to {{target}}"

# Recipe with a default value
serve port="8080":
    echo "Serving on port {{port}}"

Important: Justfile recipes use tabs for indentation, not spaces. This is the most common source of syntax errors.

Dependencies

Recipes can depend on other recipes:

build:
    echo "Building..."

test: build
    echo "Testing..."

# Run build, then test, then deploy
deploy target: build test
    echo "Deploying to {{target}}"

Variables and Environment

# Set variables
project := "my-app"
version := "1.0.0"

# Use environment variables
export DATABASE_URL := "postgres://localhost/mydb"

build:
    echo "Building {{project}} v{{version}}"

Conditional Recipes

# OS-specific commands
install:
    #!/usr/bin/env bash
    if [[ "$(uname)" == "Darwin" ]]; then
        brew install mypackage
    else
        sudo apt install mypackage
    fi

Practical Example: Dotfiles Management

A common use case is automating dotfiles deployment with Stow:

# Justfile for dotfiles repo

# Deploy shared configs to home directory
shared:
    stow -d shared -t ~ zsh git starship

# Deploy machine-specific SSH config
machine target:
    stow -d machines/{{target}} -t ~ ssh

# Deploy Docker configs to /opt (requires sudo)
docker:
    sudo stow -d machines/my-server -t / docker

# Copy configs that cannot be symlinked (e.g., unprivileged containers)
copy-configs:
    sudo cp machines/my-server/cloudflared/config.yml /opt/cloudflared/data/config.yml

# Deploy everything for a specific machine
setup target: shared (machine target)

# Lint all shell scripts
lint:
    find . -name '*.sh' -exec shellcheck {} +

Run with just shared, just setup my-server, etc.

Just vs Make

Use Just when you need a task runner. Use Make when you need file-dependency tracking (e.g., recompile only changed files).

Troubleshooting

error: Recipe line has inconsistent leading whitespace

Justfile recipes require tab indentation. If you see this error, your editor is inserting spaces. Configure your editor to use tabs for Justfiles.

just: command not found

Ensure Just is installed and on your PATH. If you installed via the install script to ~/bin, add it to your shell config:

[[ -d "$HOME/bin" ]] && export PATH="$HOME/bin:$PATH"

Recipe runs but commands are not found

By default, each line in a recipe runs in a separate shell. Use a shebang to run multi-line scripts in a single shell:

setup:
    #!/usr/bin/env bash
    set -euo pipefail
    echo "Step 1"
    echo "Step 2"

Resources

🔗

Just Manual just.systems

Complete reference for Just syntax, features, and configuration

🔗

Just on GitHub github.com

Source code, examples, and community discussions