YAML

YAML, or YAML Ain’t Markup Language, is a human-readable data serialisation language just like XML and JSON, it is often used to write configuration files. YMAL files have two extensions .yaml or .yml. YAML data structure is defined using line separation and indentation, all YAML files can optionally start with --- and end with ....

---
name: John Doe # no quotation string
age: 30
address:
  street: "123 Main St" # double quotation string
  city: Anytown
  state: CA
phone_numbers:
  - home: 555-555-5555
  - work: 555-555-1234
...

Data types

String String can be in double quotation marks (” ”), single quotation marks (’ ’), or no quotation marks

Boolean YAML indicates boolean values with the keywords True, On and Yes for true. False is indicated with False, Off, or No.

foo: True
bar: Yes
light: On

Dictionary A dictionary is represented in a key value pair form (key: value), the colon must be followed by a space.

# an employee record
martin:
  name: Martin D'vloper
  job: Developer
  skill: Elite

List List contains multiple values, all members of a list are lines at the same indentation level, starting with a dash (-) and followed by a space.

# multiple employee records
- martin:
    name: Martin D'vloper
    job: Developer
    skills:
      - python
      - perl
      - pascal
- tabitha:
    name: Tabitha Bitumen
    job: Developer
    skills:
      - lisp
      - fortran
      - erlang

Multiple lines value

Values can span multiple lines using | or >. “Literal Block Scalar” | will include the newlines and any trailing spaces, preserve the exact value. Using a “Folded Block Scalar” > will fold newlines to spaces;

include_newlines: |
            exactly as you see
            will appear these three
            lines of poetry
 
fold_newlines: >
            this is really a
            single line of text
            despite appearances
 
			start a new line

The value of include_newlines and fold_newlines would be:

exactly as you see
will appear these three
lines of poetry

this is really a single line of text despite appearances

start a new line

Additional indicators

• |- or >-: Strip the final newline.
• |+ or >+: Preserve the final newline.
• | or >: (without any additional indicators) keeps the final newline.

literal: |-
  This text will not have a trailing newline.
folded: >+
  This text will preserve the final newline (\n).

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