Use YAML with variables

Question

Are variables within YAML files possible? For example:

theme:   name: default   css_path: compiled/themes/$theme.name   layout_path: themes/$theme.name 

In this example, how can theme: name: default be used in other settings? What is the syntax?

Answer 1

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

Answer 2

After some search, I've found a cleaner solution wich use the % operator.

In your YAML file :

key : 'This is the foobar var : %{foobar}' 

In your ruby code :

require 'yaml'  file = YAML.load_file('your_file.yml')  foobar = 'Hello World !' content = file['key'] modified_content = content % { :foobar => foobar }  puts modified_content 

And the output is :

This is the foobar var : Hello World ! 

---

As @jschorr said in the comment, you can also add multiple variable to the value in the Yaml file :

Yaml :

key : 'The foo var is %{foo} and the bar var is %{bar} !' 

Ruby :

# ... foo = 'FOO' bar = 'BAR' # ... modified_content = content % { :foo => foo, :bar => bar } 

Output :

The foo var is FOO and the bar var is BAR !