04 - Conditionals

Learn how to conditionally execute steps based on system properties or variables.

What You'll Learn

• Using when for conditional execution
• OS and architecture detection
• Complex conditions with logical operators
• Combining conditionals with tags

Quick Start

cd examples/04-conditionals

# Run all steps (only matching conditions will execute)
mooncake run --config config.yml

# Run only dev-tagged steps
mooncake run --config config.yml --tags dev

What It Does

1. Demonstrates steps that always run
2. Shows OS-specific steps (macOS vs Linux)
3. Shows architecture-specific steps
4. Demonstrates tag filtering

Key Concepts

Basic Conditionals

Use when to conditionally execute steps:

- name: Linux only
  shell: echo "Running on Linux"
  when: os == "linux"

Available System Variables

• os - darwin, linux, windows
• arch - amd64, arm64, 386, etc.
• distribution - ubuntu, debian, centos, macos, etc.
• distribution_major - major version number
• package_manager - apt, yum, brew, pacman, etc.

Comparison Operators

• == - equals
• != - not equals
• >, <, >=, <= - comparisons
• && - logical AND
• || - logical OR
• ! - logical NOT

Complex Conditions

- name: ARM Mac only
  shell: echo "ARM-based macOS"
  when: os == "darwin" && arch == "arm64"

- name: High memory systems
  shell: echo "Lots of RAM!"
  when: memory_total_mb >= 16000

- name: Ubuntu 20+
  shell: apt update
  when: distribution == "ubuntu" && distribution_major >= "20"

Tags vs Conditionals

Conditionals (when): - Evaluated at runtime - Based on system facts or variables - Step-level decision making

Tags: - User-controlled filtering - Specified via CLI --tags flag - Workflow-level decision making

Testing Different Conditions

Try these commands:

# See which steps run on your system
mooncake run --config config.yml

# Preview without executing
mooncake run --config config.yml --dry-run

# Run only development steps
mooncake run --config config.yml --tags dev

Next Steps

Continue to 05-templates to learn about template rendering.