Use YAML with variables

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I had this same question, and after a lot of research, it looks like it’s not possible.

The answer from cgat is on the right track, but you can’t actually concatenate references like that.

Here are things you can do with “variables” in YAML (which are officially called “node anchors” when you set them and “references” when you use them later):

Define a value and use an exact copy of it later:

default: &default_title This Post Has No Title
title: *default_title

{ or }

example_post: &example
  title: My mom likes roosters
  body: Seriously, she does. And I don't know when it started.
  date: 8/18/2012
first_post: *example
second_post:
  title: whatever, etc.

For more info, see this section of the wiki page about YAML: http://en.wikipedia.org/wiki/YAML#References

Define an object and use it with modifications later:

default: &DEFAULT
  URL:          stooges.com
  throw_pies?:  true  
  stooges:  &stooge_list
    larry:  first_stooge
    moe:    second_stooge
    curly:  third_stooge

development:
  <<: *DEFAULT
  URL:      stooges.local
  stooges: 
    shemp: fourth_stooge

test:
  <<: *DEFAULT
  URL:    test.stooges.qa
  stooges: 
    <<: *stooge_list
    shemp: fourth_stooge

This is taken directly from a great demo here: https://gist.github.com/bowsersenior/979804

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