YAML Cheatsheet

# YAML = YAML Ain't Markup Language
# Superset of JSON (valid JSON is valid YAML)
# Uses indentation (spaces, NOT tabs)

# Key-value pairs
name: Alice
age: 30
active: true

# Nested (indent with 2 spaces)
address:
  city: NYC
  zip: "10001"

# Multiple documents in one file
---
doc1: value
---
doc2: value
...

# Strings (usually no quotes needed)
name: Alice
quoted: "hello world"
single: 'no escapes here'
with_colon: "key: value"      # quote if has :

# Numbers
integer: 42
float: 3.14
negative: -17
scientific: 1.2e+5
hex: 0xFF
octal: 0o77

# Boolean
enabled: true
disabled: false
# Also: yes/no, on/off (YAML 1.1)

# Null
value: null
also_null: ~
empty:

# Sequence (list/array)
fruits:
  - apple
  - banana
  - cherry

# Inline sequence
colors: [red, green, blue]

# Mapping (dict/object)
person:
  name: Alice
  age: 30

# Inline mapping
point: {x: 1, y: 2}

# List of objects
users:
  - name: Alice
    age: 30
  - name: Bob
    age: 25

# Nested collections
config:
  db:
    host: localhost
    port: 5432
  cache:
    - redis
    - memcached

# Literal block (|) — preserves newlines
description: |
  Line 1
  Line 2
  Line 3
# → "Line 1
Line 2
Line 3
"

# Folded block (>) — joins lines
summary: >
  This is a long
  sentence that will
  be joined.
# → "This is a long sentence that will be joined.
"

# Strip trailing newline: |-  >-
clean: |-
  No trailing newline

# Keep trailing newlines: |+  >+
keep: |+
  Extra newlines kept

# Define anchor with &
defaults: &defaults
  adapter: postgres
  host: localhost
  port: 5432

# Reference with *
development:
  database: dev_db
  <<: *defaults

production:
  database: prod_db
  <<: *defaults
  host: prod-server.com    # override

# Simple anchor
color: &main_color "#3498db"
header_bg: *main_color
button_bg: *main_color

# Type tags
explicit_string: !!str 42
explicit_int: !!int "42"
explicit_float: !!float "3.14"

# Dates
date: 2024-01-15
datetime: 2024-01-15T10:30:00Z

# Ordered mapping
ordered: !!omap
  - first: 1
  - second: 2

# Set
unique: !!set
  ? item1
  ? item2
  ? item3

# Complex keys
? [key, with, list]: value
? {complex: key}: value

# Docker Compose
services:
  web:
    image: nginx
    ports:
      - "80:80"
    volumes:
      - ./html:/usr/share/nginx/html

# GitHub Actions
name: CI
on: [push, pull_request]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npm test

# Kubernetes
apiVersion: v1
kind: Pod
metadata:
  name: web
  labels:
    app: web