Question

I know how to configure emacs to keep numbered backups. I don’t know the most canonical way to find those numbered backups.

The emacs function “find-backup-file-name” seems like it is the closest. Its documentation states:

This function computes the file name for a new backup file for filename. It may also propose certain existing backup files for deletion. find-backup-file-name returns a list whose CAR is the name for the new backup file and whose CDR is a list of backup files whose deletion is proposed.

However, this is not what I am looking for. I’m looking for a list of ALL previously created backup files. Here’s the code (paraphrased) I have written to accomplish this:

(defvar backup-directory "~/emacs.d/backups/")
(defun get-backup-pattern (file-name)
    (concat "*" (replace-regexp-in-string "\/" "\\!" file-name t t) ".~*"))

(butlast
  (split-string
    (shell-command-to-string
        (concat "find " 
                 backup-directory 
                 " -name \"" 
                 (get-backup-pattern (buffer-file-name)) 
                 "\""))
    "\n"))

This method works fine. However, shelling out to “find” seems a like a hack to me; Especially since this method is platform specific.

Is there a built-in method I should use or at least something more idiomatic?

Answer 1

So here is the solution I’ve decided on. I went away from using the *nix find command and am using directory-files as suggested.

(defun get-filter-pattern (file-name)
  (concat (replace-regexp-in-string "\/" "!" file-name t t)
      ".~[0-9]*~*$"))

(defun filter (condp lst)
  (delq nil
    (mapcar (lambda (x) (and (funcall condp x) x)) lst)))

(defun filter-files (backup-directory buffer-file-name)
  (mapcar (lambda (backup-name) (concat backup-directory backup-name))
      (filter (lambda (backup-name)
            (string-match (get-filter-pattern buffer-file-name) backup-name))
          (directory-files backup-directory))))

Perhaps this isn’t quite as optimized as using find. However, it should be platform independent (ie can use on Windows).