Justfile Creation

Guide for creating Justfiles using the just command runner.

Overview

Just is a modern command runner inspired by Make but simpler. It doesn't track file dependencies - it just runs commands. This makes it ideal for task automation without the complexity of Make.

When to Use

•Creating task runners for common operations
•Need a modern alternative to Make for non-build tasks
•Want easy argument passing to recipes
•Need cross-platform shell support
•Want simpler syntax than Make

Basic Template

justfile

# Project Configuration
project := "myproject"
version := "1.0.0"

# Default recipe (runs when no recipe specified)
default: list

# List all available recipes
list:
    @just --list

# Show help
help:
    @echo "Available recipes:"
    @just --list

# Development recipes
build:
    echo "Building {{project}}..."
    # Build commands here

test:
    echo "Running tests..."
    # Test commands here

lint:
    echo "Running linter..."
    # Lint commands here

format:
    echo "Formatting code..."
    # Format commands here

clean:
    echo "Cleaning build artifacts..."
    rm -rf build/

# Installation
install:
    echo "Installing {{project}}..."
    # Installation commands

Key Concepts

Variables

justfile

name := "myproject"
version := "1.0.0"

# Use variables with {{}}
build:
    echo "Building {{name}} v{{version}}"

Recipes (Commands)

justfile

# Simple recipe
hello:
    echo "Hello, World!"

# Recipe with arguments
greet name:
    echo "Hello, {{name}}!"

# Recipe with default argument
greet name="World":
    echo "Hello, {{name}}!"

Dependencies

justfile

# Recipe that depends on another
build: clean
    echo "Building..."

# Multiple dependencies
deploy: build test
    echo "Deploying..."

Common Patterns

Help System

justfile

# List all recipes as default
default:
    @just --list

# Or with custom formatting
help:
    @echo "Available recipes:"
    @just --list --unsorted

Environment Setup

justfile

# Check for required tools
check-tools:
    #!/usr/bin/env bash
    command -v docker >/dev/null 2>&1 || { echo "docker required"; exit 1; }
    command -v node >/dev/null 2>&1 || { echo "node required"; exit 1; }

# Setup development environment
setup: check-tools
    npm install
    echo "Setup complete"

Error Handling

justfile

# Fail on error (just does this by default)
dangerous:
    set -e
    rm -rf /important/path  # Will stop if this fails
    echo "Done"

# Continue on error
lenient:
    -rm nonexistent.txt  # The dash means ignore errors
    echo "Done"

Conditional Logic

justfile

# Check if file exists
backup file:
    #!/usr/bin/env bash
    if [[ -f "{{file}}" ]]; then
        cp "{{file}" "{{file}}.bak"
        echo "Backup created"
    else
        echo "File not found: {{file}}"
        exit 1
    fi

Platform-Specific

justfile

# Detect OS
os := `uname -s`

# Platform-specific build
build:
    #!/usr/bin/env bash
    if [[ "{{os}}" == "Darwin" ]]; then
        echo "Building for macOS..."
    else
        echo "Building for Linux..."
    fi

Best Practices

•Use default recipe - Always define what runs by default
•Provide list or help - Make recipes discoverable
•Use variables for paths, names, and configuration
•Add comments with # to document recipes
•Use set -e for bash scripts to fail fast
•Prefix with @ to suppress echoing of the command
•Use dependencies to chain operations
•Use arguments to make recipes flexible

Advanced Features

Shebang Scripts

justfile

complex-task:
    #!/usr/bin/env python3
    import os
    print(f"Current directory: {os.getcwd()}")
    print("Running Python code in just!")

Aliases

justfile

alias b := build
alias t := test

build:
    echo "Building..."

test:
    echo "Testing..."

Settings

justfile

# Set shell for all recipes
set shell := ["bash", "-cu"]

# Allow positional arguments
set positional-arguments := true

# Export variables to environment
set export := true

Dotenv Integration

justfile

# Load .env file automatically
set dotenv-load := true

# Or load specific file
set dotenv-load := "production.env"

deploy:
    echo "Deploying to {{env_var('DEPLOY_HOST')}}"

Examples

Node.js Project

justfile

# Node.js project tasks
node_version := "18"

default:
    @just --list

install:
    npm ci

dev:
    npm run dev

build:
    npm run build

test:
    npm test

lint:
    npm run lint

format:
    npm run format

clean:
    rm -rf node_modules dist/

docker-build:
    docker build -t myapp:{{node_version}} .

Rust Project

justfile

# Rust project tasks
default:
    @just --list

build:
    cargo build --release

test:
    cargo test

check:
    cargo check

fmt:
    cargo fmt

clippy:
    cargo clippy -- -D warnings

clean:
    cargo clean

doc:
    cargo doc --open

# Run with features
run *args:
    cargo run --features "dev" {{args}}

Documentation Site

justfile

# Documentation with MkDocs
default:
    @just --list

serve:
    mkdocs serve

build:
    mkdocs build

deploy: build
    mkdocs gh-deploy

clean:
    rm -rf site/

# Update dependencies
update:
    pip install -U mkdocs mkdocs-material