YAML Essentials

YAML Essentials

YAML Syntax Overview

Basic Rules

• Case sensitive
• Indentation matters
• Uses spaces (not tabs)
• Key-value pairs

Document Structure

• Start with ---
• End with ... (optional)
• Comments use #
• Hierarchical structure

Data Types and Structures

Scalars

• Strings

  name: "John Doe"
  description: 'A simple string'
  unquoted: This is also a string
  

• Numbers

  integer: 42
  float: 3.14
  scientific: 1.23e-4
  

• Booleans

  true_value: true
  false_value: false
  yes_value: yes
  no_value: no
  

Collections

Lists

fruits:
  - apple
  - banana
  - orange

# Alternative syntax
fruits: [apple, banana, orange]

Dictionaries

user:
  name: John
  age: 30
  roles:
    - admin
    - developer

# Alternative syntax
user: {name: John, age: 30}

Common YAML Patterns

Multi-line Strings

description: |
  This is a long
  multi-line string
  that preserves newlines

folded_text: >
  This is a long text
  that will be folded
  into a single line

Anchors and Aliases

defaults: &defaults
  timeout: 30
  retries: 3

webserver:
  <<: *defaults
  port: 80

YAML in Ansible

Playbook Structure

---
- name: Example Playbook
  hosts: webservers
  become: true
  tasks:
    - name: Install Apache
      yum:
        name: httpd
        state: present

Variables

vars:
  http_port: 80
  max_clients: 200

vars_files:
  - vars/common.yml
  - vars/webserver.yml

Common Mistakes

Indentation Issues

# Incorrect
tasks:
- name: Install package
yum:
    name: httpd

# Correct
tasks:
  - name: Install package
    yum:
      name: httpd

Quoting Special Characters

# Incorrect
command: echo * > output.txt

# Correct
command: "echo * > output.txt"

Best Practices

• Use consistent indentation
• Quote strings with special characters
• Use descriptive keys
• Keep files organized
• Comment complex structures

Practical Exercise

Writing a Simple YAML File

1. Create a new file
2. Define basic structures
3. Validate syntax

Common Tools

• yamllint for validation
• Online YAML validators
• Text editors with YAML support

Key Takeaways

• YAML is human-readable
• Proper indentation is crucial
• Understanding data types helps
• Practice improves proficiency

Additional Resources

• YAML Specification
• Ansible YAML Syntax
• Online YAML Validator