1 files changed, 25 insertions, 3 deletions
diff --git a/lib/expand_variables.rb b/lib/expand_variables.rb
index 3a50925d628..dc8f9d0c970 100644
--- a/lib/expand_variables.rb
+++ b/lib/expand_variables.rb
@@ -1,17 +1,39 @@
 # frozen_string_literal: true
 
 module ExpandVariables
+  VARIABLES_REGEXP = /\$([a-zA-Z_][a-zA-Z0-9_]*)|\${\g<1>}|%\g<1>%/.freeze
+
   class << self
     def expand(value, variables)
+      replace_with(value, variables) do |vars_hash, last_match|
+        match_or_blank_value(vars_hash, last_match)
+      end
+    end
+
+    def expand_existing(value, variables)
+      replace_with(value, variables) do |vars_hash, last_match|
+        match_or_original_value(vars_hash, last_match)
+      end
+    end
+
+    private
+
+    def replace_with(value, variables)
       variables_hash = nil
 
-      value.gsub(/\$([a-zA-Z_][a-zA-Z0-9_]*)|\${\g<1>}|%\g<1>%/) do
+      value.gsub(VARIABLES_REGEXP) do
         variables_hash ||= transform_variables(variables)
-        variables_hash[Regexp.last_match(1) || Regexp.last_match(2)]
+        yield(variables_hash, Regexp.last_match)
       end
     end
 
-    private
+    def match_or_blank_value(variables, last_match)
+      variables[last_match[1] || last_match[2]]
+    end
+
+    def match_or_original_value(variables, last_match)
+      match_or_blank_value(variables, last_match) || last_match[0]
+    end
 
     def transform_variables(variables)
       # Lazily initialise variables