How to use YAML Aliases
Have you ever had to copy and paste duplicate content in a YAML file and wondered if it is possible to DRY that up? As it turns out, YAML allows you to repeat nodes via aliases.
YAML Aliases allow you to assign a name to a value or block of data and recall the assigned data by its name in the YAML file. Aliases should work for any file written in YAML.
hello: &hello 'hello' greeting: audience: 'world' hello: *hello #greeting.hello has the string value of 'hello' new_greeting: audience: 'room' hello: *hello #new_greeting.hello has the string value of 'hello'
Aliasing blocks of data
Besides string or number values, you can alias a block of data as well:
foo: bar: qux: 'quxqux' baz: 'bazbaz' greeting: audience: 'world' bar: *bar #greeting.bar has the same values as foo.bar. #So greeting.bar.baz is 'bazbaz'
Modifying a section of an alias
You can copy an alias and modify a section of it by using the merge key (<<:):
bar: qux: 'quxqux' baz: 'bazbaz' greeting: audience: 'world' bar: <<: *bar # greeting.bar.qux is 'quxqux' baz: 'notbaz' # greeting.bar.baz is 'notbaz'
Defining aliases from modified aliases
You can even modify a section of an alias and define that as a new alias:
bar: qux: 'quxqux' baz: 'bazbaz' greeting: audience: 'world' bar: <<: baz: 'notbaz' new_greeting: audience: 'room' bar: *newalias #new_greeting.bar.baz is 'notbaz'
Alias nodes are described in the YAML specification here