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Backup Files

   Because Unix does not provide version numbers in file names,
rewriting a file in Unix automatically destroys all record of what the
file used to contain.  Thus, saving a file from Emacs throws away the
old contents of the file--or it would, except that Emacs carefully
copies the old contents to another file, called the "backup" file,
before actually saving.  (This assumes that the variable
`make-backup-files' is non-`nil'.  Backup files are not written if this
variable is `nil'.)

   At your option, Emacs can keep either a single backup file or a
series of numbered backup files for each file that you edit.

   Emacs makes a backup for a file only the first time the file is saved
from one buffer.  No matter how many times you save a file, its backup
file continues to contain the contents from before the file was visited.
Normally this means that the backup file contains the contents from
before the current editing session; however, if you kill the buffer and
then visit the file again, a new backup file will be made by the next

* Names
Backup NamesHow backup files are named; choosing single or numbered backup files.
* Deletion
Backup DeletionEmacs deletes excess numbered backups.
* Copying
Backup CopyingBackups can be made by copying or renaming.

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