How do I parse a YAML file in Ruby?

226
votes

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
3
rubyyaml
can you give the output of the script when you run it? files in the right place? you can always fire up a Rails console and see if ruby can see that path as well. – Lukas
Yeah, the file does exist and is in the right location. Ive updated my post with the error. – alvincrespo

3 Answers

481
votes

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"]}]}
13
votes

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

4
votes

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"}}}}}