yaml.md

YAML - Yet Another Markup Language

YAML is used for configuration by many technologies as it's easier and cleaner to read and write than JSON / XML.

• References
• Key Points
• YAML Linting
• Advanced YAML
  • Anchors and References
  • Override / Extend - Anchors and References
• Meme
  • Fixing YAML

References

https://docs.ansible.com/ansible/latest/reference_appendices/YAMLSyntax.html

https://spacelift.io/blog/yaml

https://www.educative.io/blog/advanced-yaml-syntax-cheatsheet

http://yaml.org/refcard.html

Key Points

Yaml better than JSON, adds:

• comments

• extensible data types

• relational anchors

• strings without quotation marks

• mapping types preserving key order

• must quote these constructs:

  • colon followed by space or EOL
  • string literal "True" (otherwise assumes boolean)
  • string literal "1.2" (otherwise assumes float)

- list_item1
- list_item2:
  key1: val1
  key2: val2

        |
        line1
        line2
        line3

        >
        single
        long
        line

YAML Linting

Always lint your YAML to catch otherwise hard to spot whitespace errors such as inconsistent indentation or tabs vs spaces.

From DevOps-Bash-tools, recursively find and lint all *.yaml / *,yml files:

check_yaml.sh

From DevOps-Python-tools, recursively find and lint all *.yaml / *,yml files:

validate_yaml.py .

I run these automatically in all my GitHub repos via CI/CD.

Advanced YAML

Anchors and References

Use & prefix anchor to mark a section and * to reference to it later in the same YAML to reduce duplication.

Override / Extend - Anchors and References

Prefix the *<name> reference with <<: to allow you to add more fields underneath it. Same name fields are overridden.

Meme

Fixing YAML