Yaml (Yet Another Markup Language)

calendarFeb 1, 2024 · 3 min read · Yaml

YAML (“Yet Another Markup Language”) is a human-readable data serialization language. It is commonly used for configuration files

Basic Rules

YAML is case sensitive.

YAML does not allow the use of tabs. Spaces are used instead as tabs because tabs are not universally supported.

Scalar types (Datatypes)

 1n1: 1            # integer          
 2n2: 1.234        # float      
 3
 4s1: 'abc'        # string        
 5s2: "abc"        # string           
 6s3: abc          # string           
 7
 8b: false         # boolean type 
 9
10d: 2015-04-05    # date type
11
12e: !!str 123     # a string, disambiguated by explicit type
13f: !!str Yes     # a string via explicit type
14g: !!float 123   # also a float via explicit data type prefixed by (!!)
15

Equavalent JSON

1{
2    "n1": 1,
3    "n2": 1.234,
4    "s1": "abc",
5    "s2": "abc",
6    "s3": "abc",
7    "b": false,
8    "d": "2015-04-05"
9}

Variables Reference

1some_thing: &VAR_NAME foobar
2other_thing: *VAR_NAME

Equavalent JSON

1{
2    "some_thing": "foobar",
3    "other_thing": "foobar"
4}

Sequence

1object:
2    attributes:
3        - a1
4        - a2
5        - a3
6    methods: [getter, setter]

Equavalent JSON

1{
2    "object": {
3        "attributes": ["a1", "a2", "a3"],
4        "methods": ["getter", "setter"]
5    }
6}

Sequence of sequences

1my_sequences:
2    - [1, 2, 3]
3    - [4, 5, 6]

Equavalent JSON

1{
2    "my_sequences": [
3        [1, 2, 3], 
4        [4, 5, 6]
5    ]
6}

Comments

1# A single line comment example
2
3# block level comment example
4# comment line 1
5# comment line 2
6# comment line 3

Multiline strings

1description: |
2    hello
3    world

Equavalent JSON

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

Folded text

1description: >
2    hello
3    world

Equavalent JSON

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

Hashes

1jack:
2    id: 1
3    name: Franc
4    salary: 5000
5    hobby:
6        - a
7        - b
8    loc: {country: "A", city: "A-A"}

Equavalent JSON

 1{
 2    "jack": {
 3        "id": 1,
 4        "name": "Franc",
 5        "salary": 5000,
 6        "hobby": ["a", "b"],
 7        "loc": {
 8            "country": "A", "city": "A-A"
 9        }
10    }
11}

Nested dictionaries

1Employee:
2    id: 1
3    name: "Franc"
4    department:
5        name: "Sales"
6        depid: "11"

Equavalent JSON

 1{
 2    "Employee": {
 3        "id": 1,
 4        "name": "Franc",
 5        "department": {
 6            "name": "Sales",
 7            "depid": "11"
 8        }
 9    }
10}

Sequence of dictionaries

1children:
2    - name: Jimmy Smith
3        age: 15
4    - name: Jenny Smith
5        age: 12

Equavalent JSON

1{
2    "children": [
3        {"name": "Jimmy Smith", "age": 15},
4        {"name": "Jenny Smith", "age": 12}
5    ]
6}

Set

1set1: !!set
2    ? one
3    ? two
4set2: !!set {'one', "two"}

Equavalent JSON

1{
2    "set1": {"one": null, "two": null},
3    "set2": {"one": null, "two": null}
4}

Inheritance

1parent: &defaults
2    a: 2
3    b: 3
4
5child:
6    <<: *defaults
7    b: 4

Equavalent JSON

1{
2"parent": {"a": 2, "b": 3},
3"child": {"a": 2, "b": 4}
4}

Reference

1values: &ref
2    - These values
3    - will be reused below
4
5other_values:
6    i_am_ref: *ref

Equavalent JSON

 1{
 2    "values": [
 3        "These values",
 4        "will be reused below"
 5    ],
 6    "other_values": {
 7            "i_am_ref": [
 8                "These values",
 9                "will be reused below"
10            ]
11        }
12}

Documents

1---
2document: this is doc 1
3---
4document: this is doc 2
5...