The ‘rake/clean’ file defines two file lists (CLEAN and CLOBBER) and two rake tasks (:clean and :clobber).

:clean
Clean up the project by deleting scratch files and backup files. Add files to the CLEAN file list to have the :clean target handle them.
:clobber
Clobber all generated and non-source files in a project. The task depends on :clean, so all the clean files will be deleted as well as files in the CLOBBER file list. The intent of this task is to return a project to its pristine, just unpacked state.
Required Files
Constants
CLEAN = Rake::FileList["**/*~", "**/*.bak", "**/core"]
CLOBBER = Rake::FileList.new