Make a backup before overwriting a file. Leave it around after the file has been successfully written. If you do not want to keep the backup file, but you do want a backup while the file is being written, reset this option and set the 'writebackup' option (this is the default). If you do not want a backup file at all reset both options (use this if your file system is almost full). See the backup-table for more explanations. When the 'backupskip' pattern matches, a backup is not made anyway. When 'patchmode' is set, the backup may be renamed to become the oldest version of a file. NOTE: This option is reset when 'compatible' is set.

(default off)