How do I parse a YAML file in Ruby?

I would like to know how to parse a YAML file with the following contents:

--- 
javascripts: 
- fo_global:
  - lazyload-min
  - holla-min

Currently I am trying to parse it this way:

@custom_asset_packages_yml = (File.exists?("#{RAILS_ROOT}/config/asset_packages.yml") ? YAML.load_file("#{RAILS_ROOT}/config/asset_packages.yml") : nil)
    if !@custom_asset_packages_yml.nil?
      @custom_asset_packages_yml['javascripts'].each{ |js|
        js['fo_global'].each{ |script|
         script
        }
      }
    end

But it doesn't seem to work and gives me an error that the value is nil.

You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.each

If I try this, it puts out the entire string (fo_globallazyload-minholla-min):

if !@custom_asset_packages_yml.nil?
          @custom_asset_packages_yml['javascripts'].each{ |js|
            js['fo_global']
          }
        end

Maybe I'm missing something, but why try to parse the file? Why not just load the YAML and examine the object(s) that result?

If your sample YAML is in some.yml, then this:

require 'yaml'
thing = YAML.load_file('some.yml')
puts thing.inspect

gives me

{"javascripts"=>[{"fo_global"=>["lazyload-min", "holla-min"]}]}

I had the same problem but also wanted to get the content of the file (after the YAML front-matter).

This is the best solution I have found:

if (md = contents.match(/^(?<metadata>---\s*\n.*?\n?)^(---\s*$\n?)/m))
  self.contents = md.post_match
  self.metadata = YAML.load(md[:metadata])
end

Source and discussion: https://practicingruby.com/articles/tricks-for-working-with-text-and-files

Here is the one liner i use, from terminal, to test the content of yml file(s):

$ ruby  -r yaml -r pp  -e 'pp YAML.load_file("/Users/za/project/application.yml")'
{"logging"=>
  {"path"=>"/var/logs/",
   "file"=>"TacoCloud.log",
   "level"=>
    {"root"=>"WARN", "org"=>{"springframework"=>{"security"=>"DEBUG"}}}}}