The accepted answer is good, but it can be greatly improved by additionally backing up on every save and backing up versioned files.
First, basic settings as described in the accepted answer:
(setq version-control t ;; Use version numbers for backups.
kept-new-versions 10 ;; Number of newest versions to keep.
kept-old-versions 0 ;; Number of oldest versions to keep.
delete-old-versions t ;; Don't ask to delete excess backup versions.
backup-by-copying t) ;; Copy all files, don't rename them.
Next, also backup versioned files, which Emacs does not do by default (you don't commit on every save, right?):
(setq vc-make-backup-files t)
Finally, make a backup on each save, not just the first. We make two kinds of backups:
per-session backups: once on the first save of the buffer in each Emacs session. These simulate Emac's default backup behavior.
per-save backups: once on every save. Emacs does not do this by default, but it's very useful if you leave Emacs running for a long time.
The backups go in different places and Emacs creates the backup dirs automatically if they don't exist:
;; Default and per-save backups go here:
(setq backup-directory-alist '(("" . "~/.emacs.d/backup/per-save")))
(defun force-backup-of-buffer ()
;; Make a special "per session" backup at the first save of each
;; emacs session.
(when (not buffer-backed-up)
;; Override the default parameters for per-session backups.
(let ((backup-directory-alist '(("" . "~/.emacs.d/backup/per-session")))
(kept-new-versions 3))
(backup-buffer)))
;; Make a "per save" backup on each save. The first save results in
;; both a per-session and a per-save backup, to keep the numbering
;; of per-save backups consistent.
(let ((buffer-backed-up nil))
(backup-buffer)))
(add-hook 'before-save-hook 'force-backup-of-buffer)
I became very interested in this topic after I wrote $< instead of
$@ in my Makefile, about three hours after my previous commit :P
The above is based on an Emacs Wiki page I heavily edited.