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(elisp)Backup Files

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Backup Files
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   A "backup file" is a copy of the old contents of a file you are
editing.  Emacs makes a backup file the first time you save a buffer
into its visited file.  Normally, this means that the backup file
contains the contents of the file as it was before the current editing
session.  The contents of the backup file normally remain unchanged once
it exists.

   Backups are usually made by renaming the visited file to a new name.
Optionally, you can specify that backup files should be made by copying
the visited file.  This choice makes a difference for files with
multiple names; it also can affect whether the edited file remains owned
by the original owner or becomes owned by the user editing it.

   By default, Emacs makes a single backup file for each file edited.
You can alternatively request numbered backups; then each new backup
file gets a new name.  You can delete old numbered backups when you
don't want them any more, or Emacs can delete them automatically.

Making Backups

How Emacs makes backup files, and when.

Rename or Copy

Two alternatives: renaming the old file or copying it.

Numbered Backups

Keeping multiple backups for each source file.

Backup Names

How backup file names are computed; customization.