Just

just - Command Runner

IMPORTANT: just is the PREFERRED command runner for project task automation. Use Justfiles instead of Makefiles for new projects and task automation.

Core Philosophy

• Justfiles over Makefiles: Prefer just for task automation unless working with existing Make-based projects
• Simple recipes: Keep recipe definitions concise and readable
• Delegate to scripts: For complex logic, call external scripts rather than embedding in recipes
• Just as orchestrator: Use just to coordinate and invoke scripts, not to contain business logic

Basic Usage Patterns

Running Recipes

# List available recipes
just --list
just -l

# Run a recipe
just build
just test

# Run recipe with arguments
just deploy production
just run-test integration

# Run recipe from different directory
just --working-directory /path/to/project build

# Choose a different Justfile
just --justfile custom.just build

Recipe Definition Basics

# Simple recipe
build:
    cargo build --release

# Recipe with description (shown in --list)
# Run all tests
test:
    cargo test --quiet

# Recipe with dependencies (runs setup first)
deploy: build test
    ./scripts/deploy.sh

# Recipe with parameters
run-test test_name:
    cargo test {{test_name}}

# Recipe with default parameter value
serve port="8080":
    python -m http.server {{port}}

# Recipe with multiple parameters
deploy env branch="main":
    ./scripts/deploy.sh {{env}} {{branch}}

Delegation Pattern (PREFERRED)

Good - Delegates to script:

# Build the project
build:
    ./scripts/build.sh

# Run integration tests
test-integration:
    ./scripts/test-integration.sh

# Deploy to environment
deploy env:
    ./scripts/deploy.sh {{env}}

Avoid - Complex logic in recipe:

# ❌ Too complex - should be in a script
deploy env:
    #!/usr/bin/env bash
    set -euo pipefail
    if [ "{{env}}" = "production" ]; then
        echo "Deploying to production..."
        git fetch origin
        git checkout main
        git pull
        docker build -t app:latest .
        docker push registry.example.com/app:latest
        kubectl apply -f k8s/production/
        kubectl rollout status deployment/app
    else
        echo "Deploying to staging..."
        # ... many more lines ...
    fi

Better - Simple orchestration:

# Deploy to production
deploy-prod:
    ./scripts/deploy.sh production

# Deploy to staging
deploy-staging:
    ./scripts/deploy.sh staging

# Generic deploy with validation
deploy env:
    ./scripts/validate-env.sh {{env}}
    ./scripts/deploy.sh {{env}}

Recipe Features

Dependencies

# Recipe runs after its dependencies
all: clean build test deploy

# Dependencies run in order specified
deploy: build test package
    ./scripts/deploy.sh

# Multiple dependency chains
full-deploy: lint build test docker-build docker-push k8s-deploy

Variables

# Set variables at top of file
version := "1.2.3"
registry := "registry.example.com"
image := registry + "/app:" + version

# Use in recipes
docker-build:
    docker build -t {{image}} .

docker-push:
    docker push {{image}}

# Environment variables
deploy:
    API_KEY=$API_KEY ./scripts/deploy.sh

Conditional Execution

# Use shell conditionals in scripts
test:
    ./scripts/test.sh

# Or delegate to script
check-and-test:
    ./scripts/check-and-test.sh

Private Recipes

# Private recipe (not shown in --list, can't be run directly)
_setup:
    ./scripts/setup-env.sh

# Public recipe uses private recipe
deploy: _setup
    ./scripts/deploy.sh

Recipe Attributes

# Ignore errors (continue even if fails)
[ignore-errors]
lint:
    ./scripts/lint.sh

# Run in specific directory
[working-directory: 'frontend']
build-ui:
    npm run build

# Confirm before running
[confirm]
deploy-prod:
    ./scripts/deploy.sh production

# Don't print recipe before running
[no-quiet]
status:
    ./scripts/status.sh

Common Patterns

Development Workflow

# Default recipe (runs when you type 'just')
default: check test

# Quick validation
check:
    ./scripts/check.sh

# Run all tests
test:
    ./scripts/test.sh

# Full CI workflow
ci: check test lint build

Build Automation

# Clean build artifacts
clean:
    ./scripts/clean.sh

# Build project
build:
    ./scripts/build.sh

# Full rebuild
rebuild: clean build

# Build with caching
build-cached:
    ./scripts/build.sh --cache

Multi-Environment Deployment

# Development environment
dev:
    ./scripts/run-dev.sh

# Staging deployment
deploy-staging:
    ./scripts/deploy.sh staging

# Production deployment (with confirmation)
[confirm]
deploy-prod:
    ./scripts/deploy.sh production

# Deploy to any environment
deploy env:
    ./scripts/validate-env.sh {{env}}
    ./scripts/deploy.sh {{env}}

Docker Workflows

# Build Docker image
docker-build:
    ./scripts/docker-build.sh

# Run container locally
docker-run:
    ./scripts/docker-run.sh

# Push to registry
docker-push: docker-build
    ./scripts/docker-push.sh

# Complete Docker workflow
docker: docker-build docker-push

Database Operations

# Run migrations
migrate:
    ./scripts/db-migrate.sh

# Rollback migration
migrate-rollback:
    ./scripts/db-rollback.sh

# Seed database
seed:
    ./scripts/db-seed.sh

# Reset database (dev only)
[confirm]
db-reset:
    ./scripts/db-reset.sh

Script Organization

Recommended Structure

project/
├── justfile
├── scripts/
│   ├── build.sh
│   ├── test.sh
│   ├── deploy.sh
│   ├── validate-env.sh
│   └── utils/
│       ├── common.sh
│       └── logging.sh
└── src/
    └── ...

Script Best Practices

Make scripts executable:

chmod +x scripts/*.sh

Use shebang in scripts:

#!/usr/bin/env bash
set -euo pipefail

# Script logic here

Keep scripts focused:

# Good - single purpose
# scripts/build.sh
#!/usr/bin/env bash
set -euo pipefail

echo "Building project..."
cargo build --release

Source common utilities:

# scripts/deploy.sh
#!/usr/bin/env bash
set -euo pipefail

source "$(dirname "$0")/utils/common.sh"
source "$(dirname "$0")/utils/logging.sh"

log_info "Starting deployment..."
# Deployment logic

Advanced Features

Command Evaluation

# Backticks execute shell commands
commit := `git rev-parse --short HEAD`
timestamp := `date +%Y%m%d-%H%M%S`

# Use in recipes
tag:
    echo "Tagging {{commit}} at {{timestamp}}"

Multi-line Constructs

# Multi-line variables
help := '''
  Available commands:
    build  - Build the project
    test   - Run tests
    deploy - Deploy to production
'''

# Print help
help:
    @echo {{help}}

Settings

# Change shell (default is sh)
set shell := ["bash", "-c"]

# Make all recipes silent (@echo becomes echo)
set quiet := true

# Use PowerShell on Windows
set windows-shell := ["powershell.exe", "-c"]

# Use Python for recipes
set shell := ["python3", "-c"]

Imports

# Import recipes from other files
import 'ci.just'
import 'deploy.just'

# Use imported recipes
all: ci-check deploy-staging

Gotcha — redefining an imported recipe is a hard error, not a silent override. Defining a local recipe with the same name as one pulled in via import/import? fails by default, regardless of definition order:

error: Recipe `render` first defined on line 8 is redefined on line 46

To make a local recipe actually replace an imported one, opt in with set allow-duplicate-recipes := true and define the local recipe before the import line — just uses whichever definition it sees first once duplicates are allowed:

set allow-duplicate-recipes := true

render:
    echo "local override wins"

import? 'canonical.just'  # also defines `render`, but this one loses

This setting is only needed when replacing a recipe's behavior under the same name. Adding a new, differently-named recipe alongside imported ones needs no special setting — only same-name conflicts are affected.

Integration with Other Tools

With Cargo (Rust)

# Rust development workflow
check:
    cargo check --quiet

test:
    cargo test --quiet

clippy:
    cargo clippy

build: check test clippy
    cargo build --release

# Or delegate to script
rust-workflow:
    ./scripts/rust-workflow.sh

With npm/pnpm/yarn

# Install dependencies
install:
    pnpm install

# Run dev server
dev:
    pnpm run dev

# Build frontend
build:
    pnpm run build

# Or use scripts
ui-build:
    ./scripts/build-ui.sh

With Docker

# Docker operations via scripts
docker-build:
    ./scripts/docker/build.sh

docker-run:
    ./scripts/docker/run.sh

docker-compose-up:
    docker-compose up -d

With Git

# Git workflow helpers
sync:
    git fetch origin
    git pull

push: test
    git push origin main

release version:
    ./scripts/release.sh {{version}}

Complete Workflow Examples

Workflow 1: Web Application

# Default - run dev server
default: dev

# Install dependencies
install:
    ./scripts/install.sh

# Development server
dev:
    ./scripts/dev.sh

# Run tests
test:
    ./scripts/test.sh

# Build for production
build:
    ./scripts/build.sh

# Deploy to staging
deploy-staging: test build
    ./scripts/deploy.sh staging

# Deploy to production
[confirm]
deploy-prod: test build
    ./scripts/deploy.sh production

Workflow 2: Rust Project

# Default - check code
default: check

# Fast check
check:
    cargo check --quiet

# Run tests
test:
    cargo test --quiet

# Lint code
lint:
    cargo clippy

# Full validation
ci: test lint
    ./scripts/verify-formatting.sh

# Build release
build:
    cargo build --release

# Install binary
install: build
    cargo install --path .

Workflow 3: Monorepo

# Build all services
build-all:
    ./scripts/build-all.sh

# Test all services
test-all:
    ./scripts/test-all.sh

# Build specific service
build-service service:
    ./scripts/build-service.sh {{service}}

# Deploy specific service
deploy service env:
    ./scripts/deploy-service.sh {{service}} {{env}}

# Full deployment
deploy-all env: test-all build-all
    ./scripts/deploy-all.sh {{env}}

Common Commands Quick Reference

# List recipes
just --list

# Run recipe
just <recipe>

# Run with arguments
just <recipe> arg1 arg2

# Set variable
just var=value recipe

# Choose Justfile
just --justfile path/to/justfile recipe

# Work in different directory
just --working-directory /path recipe

# Dry run (show what would run)
just --dry-run recipe

# Verbose output
just --verbose recipe

# Choose recipe interactively
just --choose

Best Practices Summary

1. Keep recipes simple: 1-3 lines max; delegate complex logic to scripts
2. Use descriptive names: deploy-prod not dp, test-integration not ti
3. Add comments: Describe what each recipe does
4. Organize scripts: Keep scripts in scripts/ directory with logical subdirectories
5. Make scripts executable: Use chmod +x scripts/*.sh
6. Use dependencies: Chain recipes with dependencies rather than duplicating commands
7. Confirm destructive operations: Use [confirm] for deployments, database resets, etc.
8. Private recipes for setup: Use _recipe naming for internal setup steps
9. Default recipe: Provide sensible default (usually dev or check)
10. Document in comments: Add comments explaining complex workflows

When to Use Scripts vs. Recipes

Use Recipe Directly:

• Single command execution
• Simple chaining (3 commands or less)
• Setting environment variables for a command
• Quick aliases

Use Script (PREFERRED for most cases):

• Complex conditional logic
• Multiple steps with error handling
• Reusable logic across recipes
• Long command sequences (>3 commands)
• Anything requiring significant bash scripting

Justfile Template

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

# Variables
version := "1.0.0"

# Default recipe
default: check

# List all recipes
help:
    @just --list

# Development
dev:
    ./scripts/dev.sh

# Testing
test:
    ./scripts/test.sh

# Build
build:
    ./scripts/build.sh

# Full CI check
ci: test build
    ./scripts/verify.sh

# Deploy to staging
deploy-staging: ci
    ./scripts/deploy.sh staging

# Deploy to production
[confirm]
deploy-prod: ci
    ./scripts/deploy.sh production

# Clean build artifacts
clean:
    ./scripts/clean.sh

Migration from Make

Key Differences from Make

1. Not a build system: just is for running commands, not tracking file dependencies
2. Recipes always run: Unlike Make targets, recipes run every time (no file timestamp checking)
3. Simpler syntax: No need for .PHONY, tabs vs. spaces issues, etc.
4. Better error messages: Clear, helpful error output

Converting Makefile to Justfile

Makefile:

.PHONY: build test deploy

build:
	cargo build --release

test:
	cargo test

deploy: build test
	./deploy.sh

Justfile:

build:
    cargo build --release

test:
    cargo test

deploy: build test
    ./scripts/deploy.sh

Resources

• Official documentation: https://just.systems
• GitHub repository: https://github.com/casey/just
• Installation: brew install just (macOS) or cargo install just