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From: jr@bbn.com (John Robinson)
Newsgroups: comp.emacs
Subject: Re: how to change backup file names?
Message-ID: <34831@bbn.COM>
Date: 19 Jan 89 22:09:29 GMT
References: <2926@uvacs.cs.Virginia.EDU> <8776@megaron.arizona.edu> <47991@yale-celray.yale.UUCP>
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Reply-To: jr@bbn.com (John Robinson)
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In-reply-to: Ram-Ashwin@cs.yale.edu (Ashwin Ram)

In article <47991@yale-celray.yale.UUCP>, Ram-Ashwin@cs (Ashwin Ram) writes:
>Hmmm... an 'apropos' on 'backup' reveals:
>
>    find-backup-file-name:
>
>and:
>
>    make-backup-file-name:
>
>Why are there two functions?  Does one call the other?  Which is the right
>one to redefine for customization?

A find-emacs-tag on one of these gets you to files.el, which has:

(defun make-backup-file-name (file)
  "Create the non-numeric backup file name for FILE.
This is a separate function so you can redefine it for customization."
  (concat file "~"))

;[... other defun deleted]

(defun find-backup-file-name (fn)
  "Find a file name for a backup file, and suggestions for deletions.
Value is a list whose car is the name for the backup file
 and whose cdr is a list of old versions to consider deleting now."
  (if (eq version-control 'never)
      (list (make-backup-file-name fn))
    (let* ((base-versions (concat (file-name-nondirectory fn) ".~"))
	   (bv-length (length base-versions))

;...

So the former (of Ashwin's list) calls the latter.  Redefining the
former is sufficient, unless you want to change the way
version-controlled backups look.  Version-control creates file
versions using backups of the form foo.~1~, foo.~2~, etc.  foo~ is
linked to the most recent backup.  More in the manual.

I think version-control will someday be part of GNU (the operating
system), so changing the form of these files if you use them may be a
little more serious departure from common practice.
--
/jr
jr@bbn.com or bbn!jr