Question

I modified my .emacs file to make auto-backups hidden files via the following code:

(defun make-backup-file-name (filename)
  (expand-file-name
   (concat "." (file-name-nondirectory filename) "~")
   (file-name-directory filename)))

It works great except that backups of hidden-files go from “.hidden-file.xxx” to “..no-longer-hidden-file.xxx’

I know zero Lisp, can someone give me a quick work-around like:

(if (filename) doesn't-start-with "."
  (concat 
  (else do-nothing))

Answer 1

You could use (equal (string-to-char filename) ?.). This turns the filename string into its first character and compares it to ?., which is the character notation for a ..

By the looks of it, you want to check (file-name-nondirectory filename) rather than just filename, so the whole statement would be something like:

(if (equal (string-to-char (file-name-nondirectory filename)) ?.)
    (concat (file-name-nondirectory filename) "~")
    (concat "." (file-name-nondirectory filename) "~"))

So the whole function should look something like:

(defun make-backup-file-name (filename)
  (expand-file-name
  (if (equal (string-to-char (file-name-nondirectory filename)) ?.)
    (concat (file-name-nondirectory filename) "~")
    (concat "." (file-name-nondirectory filename) "~"))
  (file-name-directory filename)))

You need to do a concat in both branches because you always want to append a ~.