How to lint YAML files, preferably in Ruby

Question

How do I lint YAML files, without having to upload it to http://yamllint.com ?

For example, if I have

people:
  1:
    :name: John Smith
    :name: Jane Smith

How do I make it warn me that the last :name over-writes the first :name?

I'm using Ruby 2.1, and Ubuntu 12.04.

Answer 1

The yamllint command-line tool does what you want:

sudo pip install yamllint

Specifically, it has a rule key-duplicates that detects repetitions and keys over-writing one another:

$ yamllint test.yml
test.yml
  1:1       warning  missing document start "---"  (document-start)
  4:5       error    duplication of key ":name" in mapping  (key-duplicates)

(It has many other rules that you can enable/disable or tweak.)

Answer 2

Is this what you're after?

require 'yaml'

def check_yaml(filename)
  unless YAML.dump(YAML.load_file(filename)) == File.read(filename).gsub(/\s*#.*/, '')
    raise 'problem' 
  end
end

check_yaml 'somefile.yml'