YAML cheatsheet

YAML is a data serialisation language designed to be directly writable and readable by humans

• YAML does not allow the use of tabs
• Must be space between the element parts
• YAML is CASE sensitive
• End your YAML file with the .yaml or .yml extension
• YAML is a superset of JSON
• Ansible playbooks are YAML files

some_thing: &VAR_NAME foobar
other_thing: *VAR_NAME

#↓ Equivalent JSON

{
  "some_thing": "foobar",
  "other_thing": "foobar"
}

# A single line comment example

# block level comment example
# comment line 1
# comment line 2
# comment line 3

description: |
  hello
  world

#↓ Equivalent JSON

{ "description": "hello\nworld\n" }

description: >
  hello world

#↓ Equivalent JSON

{ "description": "hello world\n" }

---
document: this is doc 1
---
document: this is doc 2

YAML uses --- to separate directives from document content.

- Mark McGwire
- Sammy Sosa
- Ken Griffey

#↓ Equivalent JSON

[
  "Mark McGwire",
  "Sammy Sosa",
  "Ken Griffey"
]

hr:  65       # Home runs
avg: 0.278    # Batting average
rbi: 147      # Runs Batted In

#↓ Equivalent JSON

{
  "hr": 65,
  "avg": 0.278,
  "rbi": 147
}

attributes:
  - a1
  - a2
methods: [getter, setter]

#↓ Equivalent JSON

{
  "attributes": ["a1", "a2"],
  "methods": ["getter", "setter"]
}

children:
  - name: Jimmy Smith
    age: 15
  - name: Jimmy Smith
    age: 15
  -
    name: Sammy Sosa
    age: 12

#↓ Equivalent JSON

{
  "children": [
    {"name": "Jimmy Smith", "age": 15},
    {"name": "Jimmy Smith", "age": 15},
    {"name": "Sammy Sosa", "age": 12}
  ]
}

my_sequences:
  - [1, 2, 3]
  - [4, 5, 6]
  -
    - 7
    - 8
    - 9
    - 0 

#↓ Equivalent JSON

{
  "my_sequences": [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9, 0]
  ]
}

Mark McGwire: { hr: 65, avg: 0.278 }
Sammy Sosa: { hr: 63, avg: 0.288 }

#↓ Equivalent JSON

{
  "Mark McGwire": {
    "hr": 65,
    "avg": 0.278
  },
  "Sammy Sosa": {
    "hr": 63,
    "avg": 0.288
  }
}

Jack:
  id: 1
  name: Franc
  salary: 25000
  hobby:
    - a
    - b
  location: { country: "A", city: "A-A" }

#↓ Equivalent JSON

{
  "Jack": {
    "id": 1,
    "name": "Franc",
    "salary": 25000,
    "hobby": ["a", "b"],
    "location": {
      "country": "A",
      "city": "A-A"
    }
  }
}

set1: !!set
  ? one
  ? two
set2: !!set { "one", "two" }

#↓ Equivalent JSON

{
  "set1": { "one": null, "two": null },
  "set2": { "one": null, "two": null }
}

Sets are represented as a Mapping where each key is associated with a null value

ordered: !!omap
  - Mark McGwire: 65
  - Sammy Sosa: 63
  - Ken Griffy: 58

#↓ Equivalent JSON

{
  "ordered": [
    { "Mark McGwire": 65 },
    { "Sammy Sosa": 63 },
    { "Ken Griffy": 58 }
  ]
}

• Sequences aka arrays or lists
• Scalars aka strings or numbers
• Mappings aka hashes or dictionaries

Based on the YAML.org refcard.