Check that variables are lowercase

lib/puppet-lint/plugins/check_variables.rb

@@ -17,3 +17,21 @@ def check
     end
   end
 end
+
+PuppetLint.new_check(:variable_is_lowercase) do
+  VARIABLE_TYPES = Set[:VARIABLE, :UNENC_VARIABLE]
+
+  def check
+    tokens.select { |r|
+      VARIABLE_TYPES.include? r.type
+    }.each do |token|
+      if token.value.gsub(/\[.+?\]/, '').match(/[A-Z]/)
+        notify :warning, {
+          :message => 'variable contains an uppercase letter',
+          :line    => token.line,
+          :column  => token.column,
+        }
+      end
+    end
+  end
+end

spec/puppet-lint/plugins/check_variables/variable_is_lowercase_spec.rb

@@ -0,0 +1,25 @@
+require 'spec_helper'
+
+describe 'variable_is_lowercase' do
+  let(:msg) { 'variable contains an uppercase letter' }
+
+  context 'a variable containing an uppercase letter' do
+    let(:code) { '$fooBar' }
+
+    it 'should only detect a single problem' do
+      expect(problems).to have(1).problem
+    end
+
+    it 'should create a warning' do
+      expect(problems).to contain_warning(msg).on_line(1).in_column(1)
+    end
+  end
+
+  context 'a variable containing only lowercase letters' do
+    let(:code) { '$foobar' }
+
+    it 'should not detect any problems' do
+      expect(problems).to have(0).problems
+    end
+  end
+end