What is YAML?

• YAML is a data format for similar purpose as XML and JSON.
• YAML syntax is indentation based, similar to python. [see Python 3 Tutorial]
• YAML file has file extension “.yml”.

Sample YAML file, used by Google App Engine:

application: helloworld
version: 1
runtime: python27
api_version: 1
threadsafe: true

handlers:
- url: /.*
  script: helloworld.app

Another Sample YAML file, from Wikipedia:

---
receipt:     Oz-Ware Purchase Invoice
date:        2007-08-06
customer:
    given:   Dorothy
    family:  Gale

items:
    - part_no:   A4786
      descrip:   Water Bucket (Filled)
      price:     1.47
      quantity:  4

    - part_no:   E1628
      descrip:   High Heeled "Ruby" Slippers
      size:      8
      price:     100.27
      quantity:  1

bill-to:  &id001
    street: |
            123 Tornado Alley
            Suite 16
    city:   East Centerville
    state:  KS

ship-to:  *id001

specialDelivery:  >
    Follow the Yellow Brick
    Road to the Emerald City.
    Pay no attention to the
    man behind the curtain.
...

another example, for setting up mongodb.

development:
  sessions:
    default:
      database: xyz_dev
      hosts:
        - localhost:27017

production:
  sessions:
    default:
      database: xyz_prod
      hosts:
        - localhost:27017
      username: <%= ENV['MONGOID_USERNAME'] %>
      password: <%= ENV['MONGOID_PASSWORD'] %>