Environment.execute() expands $ variable references recursively

lib/rscons/environment.rb

@@ -48,7 +48,26 @@ module Rscons
     end
 
     def execute(short_desc, command)
-      command = command.flatten
+      expand_varref = proc do |varref|
+        if varref.is_a?(Array)
+          varref.map do |ent|
+            expand_varref.call(ent)
+          end
+        else
+          if varref[0] == '$'
+            varname = varref[1, varref.size]
+            varval = self[varname]
+            if varval
+              expand_varref.call(varval)
+            else
+              raise "Could not find variable #{varname.inspect}"
+            end
+          else
+            varref
+          end
+        end
+      end
+      command = expand_varref.call(command.flatten).flatten
       if @echo == :command
         puts command.join(' ')
       elsif @echo == :short