Do we have an undo in Linux? I renamed a few files in one batch script. Is there a way to undo the changes without having to rename them back? Does Linux provide some native way of `undo`ing?

Linux (like other unices) doesn't natively provide an undo feature. The philosophy is that if it's gone, it's gone. If it was important, it should have been backed up.

There is a fuse filesystem that automatically keeps copies of old versions: copyfs. Of course, that can use a lot of resources. Unfortunately, it's unmaintained. Gitfs might be an alternative, I've never tried it.

The best way to protect against such accidents is to use a version control system (cvs, bazaar, darcs, git, mercurial, subversion, ...). It takes a little time to learn, but it pays off awesomely in the medium and long term.