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Single or Numbered Backups
If you choose to have a single backup file (this is the default),
the backup file's name is constructed by appending `~' to the file name
being edited; thus, the backup file for `eval.c' would be `eval.c~'.
If you choose to have a series of numbered backup files, backup file
names are made by appending `.~', the number, and another `~' to the
original file name. Thus, the backup files of `eval.c' would be called
`eval.c.~1~', `eval.c.~2~', and so on, through names like
`eval.c.~259~' and beyond.
If protection stops you from writing backup files under the usual
names, the backup file is written as `%backup%~' in your home directory.
Only one such file can exist, so only the most recently made such
backup is available.
The choice of single backup or numbered backups is controlled by the
variable `version-control'. Its possible values are
Make numbered backups.
Make numbered backups for files that have numbered backups already.
Otherwise, make single backups.
Do not in any case make numbered backups; always make single
You can set `version-control' locally in an individual buffer to
control the making of backups for that buffer's file. For example,
Rmail mode locally sets `version-control' to `never' to make sure that
there is only one backup for an Rmail file. Note: Locals.
If you set the environment variable `VERSION_CONTROL', to tell
various GNU utilities what to do with backup files, Emacs also obeys the
environment variable by setting the Lisp variable `version-control'
accordingly at startup. If the environment variable's value is `t' or
`numbered', then `version-control' becomes `t'; if the value is `nil'
or `existing', then `version-control' becomes `nil'; if it is `never'
or `simple', then `version-control' becomes `never'.
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