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Short introduction to YAML

YAML is used to describe key-value maps and arrays. YAML files are recognized by the .yml or .yaml file suffix.

A YAML dataset can be

  • a value
value
  • an array
- value 1
- value 2
- value 3

or

[value 1, value 2, value 3]
  • a dictionary
key: value
another_key: another value

or

key:
  value
another_key:
  another value
  • YAML dataset
key:
  - value 1
  - another key:
      yet another key: value 2
    another key 2:
      - more values
    this keys value is also an array:
    - but indentation is not necessary here

Values can be input across multiple lines using >:

key: >
  Here's a value that is written over multiple lines
  but is actually still considered a single line until now.

  Placing double newline here will result in newline in the actual data.

Verbatim style is supported with the | character:

key: |
  Now each
  newline is
  treated as such

YAML vs JSON

YAML is a superset of JSON (JavaScript Object Notation). Thus,

{
  "key": [
    {
      "value 1": {
        "another key": {
          "yet another key": "value 2"
        },
        "another key 2": [
          "more values"
        ],
        "this keys value is also an array": ["but indentation is not necessary here"]
      }
    }
  ]
}

is also valid YAML. In general YAML is more compact than JSON:

key:
  - value 1:
      another key:
        yet another key: value 2
      another key 2:
        - more values
      this keys value is also an array:
        - but indentation is not necessary here

yq command line tool

yq is a useful tool to work with yaml. It can be installed using pip:

$ pip show yq  
Name: yq
Version: 3.0.2
Summary: Command-line YAML/XML processor - jq wrapper for YAML/XML documents
Home-page: https://github.com/kislyuk/yq
Author: Andrey Kislyuk
Author-email: kislyuk@gmail.com
License: Apache Software License
Location: /home/jtahir/Documents/csc-stuff/osclient/lib/python3.6/site-packages
Requires: argcomplete, PyYAML, toml, xmltodict
Required-by:

yq is a jq wrapper, this means that it converts the yaml input to json and then handles the processing to jq, for this reason it has the same syntax as jq. In the example below, the value of .data.WebHookSecretKey is retrieved in raw mode (without quotes):

$ echo 'apiVersion: v1
kind: Secret
data:
  WebHookSecretKey: dGhpc19pc19hX2JhZF90b2tlbgo=
metadata:
  name: webhooksecret
  namespace: mynamespace     # set this to your project namespace
' | yq ' .data.WebHookSecretKey ' -r
dGhpc19pc19hX2JhZF90b2tlbgo=

For more information, see yaml.org or json.org.