YAML: a one-minute reference

CWL packages and job files in this module use YAML. You only need three structures to read the example.

Values and maps

Write key: value, with a space after the colon. Indentation nests values under a parent key; use spaces, not tabs.

geotiff:
  value: https://example.org/image.tif

Here geotiff is a map containing a value string. This matches the lesson's URI record input. A bare geotiff: https://example.org/image.tif would have a different type.

Lists

A dash introduces a list item. Brackets are a compact alternative:

arguments:
  - bounds
# Equivalent: arguments: [bounds]

The package's $graph is a list of process descriptions, including the workflow and tool.

Quotes and comments

Quote values when punctuation or an intended string type could be ambiguous. In particular, quote a fragment such as '#URI': an unquoted # following whitespace starts a comment.

cwlVersion: v1.2
input_type: '#URI'  # A schema reference represented as a string
version_label: '1.0.0'

true is a boolean and 42 is a number; '42' is a string. Preserve the type expected by the CWL input.

Return to the example. See the YAML specification for the full syntax.