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The functions in this section are documented mainly because you can customize the naming conventions for backup files by redefining them. If you change one, you probably need to change the rest.
This function returns a non-nil
value if filename is a
possible name for a backup file. A file with the name filename
need not exist; the function just checks the name.
(backup-file-name-p "foo") ⇒ nil
(backup-file-name-p "foo~") ⇒ 3
The standard definition of this function is as follows:
(defun backup-file-name-p (file) "Return non-nil if FILE is a backup file \ name (numeric or not)..." (string-match "~$" file))
Thus, the function returns a non-nil
value if the file name ends
with a ‘~’. (We use a backslash to split the documentation
string’s first line into two lines in the text, but produce just one
line in the string itself.)
This simple expression is placed in a separate function to make it easy to redefine for customization.
This function returns a string that is the name to use for a non-numbered backup file for file filename. On Unix, this is just filename with a tilde appended.
The standard definition of this function is as follows:
(defun make-backup-file-name (file) "Create the non-numeric backup file name for FILE. …" (concat file "~"))
You can change the backup-file naming convention by redefining this
function. The following example redefines make-backup-file-name
to prepend a ‘.’ in addition to appending a tilde:
(defun make-backup-file-name (filename) (concat "." filename "~"))
(make-backup-file-name "backups.texi") ⇒ ".backups.texi~"
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.
Two variables, kept-old-versions
and kept-new-versions
,
determine which backup versions should be kept. This function keeps
those versions by excluding them from the CDR of the value.
See Numbered Backups.
In this example, the value says that ~rms/foo.~5~ is the name to use for the new backup file, and ~rms/foo.~3~ is an “excess” version that the caller should consider deleting now.
(find-backup-file-name "~rms/foo") ⇒ ("~rms/foo.~5~" "~rms/foo.~3~")
This function returns the name of the most recent backup file for
filename, or nil
if that file has no backup files.
Some file comparison commands use this function so that they can automatically compare a file with its most recent backup.
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