# File lib/spring/client/binstub.rb, line 75
        def add
          if existing
            if existing.include?(OLD_BINSTUB)
              fallback = existing.match(/#{Regexp.escape OLD_BINSTUB}\n(.*)else/m)[1]
              fallback.gsub!(/^  /, "")
              fallback = nil if fallback.include?("exec")
              generate(fallback)
              status "upgraded"
            elsif existing.include?(LOADER)
              status "spring already present"
            elsif existing =~ BINSTUB_VARIATIONS
              upgraded = existing.sub(BINSTUB_VARIATIONS, LOADER)
              File.write(command.binstub, upgraded)
              status "upgraded"
            else
              head, shebang, tail = existing.partition(SHEBANG)

              if shebang.include?("ruby")
                unless command.binstub.exist?
                  FileUtils.touch command.binstub
                  command.binstub.chmod 0755
                end

                File.write(command.binstub, "#{head}#{shebang}#{LOADER}#{tail}")
                status "spring inserted"
              else
                status "doesn't appear to be ruby, so cannot use spring", $stderr
                exit 1
              end
            end
          else
            generate
            status "generated with spring"
          end
        end