rails 3, how use an ENV config vars in a Settings.yml file?

use following:-

 default:
       cv1: Foo
       cv2: <%= ENV['FOOVAR'] %>

The above solution did not work for me. However, I found the solution on How do I use variables in a YAML file?

My .yml file contained something like:

development:
gmail_username: <%= ENV["GMAIL_USERNAME"] %>
gmail_password: <%= ENV["GMAIL_PASSWORD"] %>

The solution looks like:

template = ERB.new File.new("path/to/config.yml.erb").read
processed = YAML.load template.result(binding)

So when you introduce a scriptlet tag in .yml file, it is more of erb template. So read it as a erb template first and then load the yml as shown above.

Use <%= ENV['FOOVAR'] %> instead of <% ENV['FOOVAR'] %>.

Be aware that this approach will only work if whatever is parsing the Yaml file is set up to process it via Erb (for example, you can see how Mongoid does exactly this). It's not universally supported in Yaml files though, so it depends on what you're using this Yaml file for.