# File lib/dotenv/substitutions/variable.rb, line 21
        def call(value, env, is_load)
          combined_env = if is_load
                           env.merge(ENV)
                         else
                           ENV.to_h.merge(env)
                         end
          value.gsub(VARIABLE) do |variable|
            match = $LAST_MATCH_INFO
            substitute(match, variable, combined_env)
          end
        end