Ray on Emacs: Emacs Numbered Backup Strategy

Emacs produces a backup of each file by default. It does this by appending a tilde to the file's name. For example, Myfile.txt is backed up to Myfile.txt~. It's a reasonable strategy, assuming that a Version Control system is in place.

But in the absence of version control, you're limited to restoring just the previous version; older versions need to be restored from backup.

I use git for coding projects that I share to the public. But I didn't create a repository for my home directory. So when C-c a m TAG¹ generated an error instead of a list of TAGged items, I hoped fervently that the latest init file change was to blame.

After finding and fixing the problem quickly, (and realizing I was lucky this time), I resolved to be more diligent about disaster recovery. I looked into what backup schemes Emacs already provides.

Emacs can create unique backups for a file rather than overwriting the previous backup. When Emacs sees a numbered backup for a given file, it will make a new, sequentially-named file for each backup of that file, while continuing to use the "append tilde" method for other files.

Once I renamed (or copied) .emacs~ to .emacs.~1~, Emacs created backups named .emacs.~2~, .emacs.~3~ (and so on). I didn't even need to change a variable -- when Emacs detected .emacs.~1~, it knew that backups of .emacs needed to be numeric, so it acted accordingly. Emacs continues to use bills.org~ as the backup for bills.org. Until I tell it otherwise.