List of directories for the backup file, separated with commas.

• The backup file will be created in the first directory in the list where this is possible. The directory must exist, Vim will not create it for you.
• Empty means that no backup file will be created ('patchmode' is impossible!). Writing may fail because of this.
• A directory "." means to put the backup file in the same directory as the edited file.
• A directory starting with "./" (or "." for MS-Windows) means to put the backup file relative to where the edited file is. The leading "." is replaced with the path name of the edited file. ("." inside a directory name has no special meaning).
• Spaces after the comma are ignored, other spaces are considered part of the directory name. To have a space at the start of a directory name, precede it with a backslash.
• To include a comma in a directory name precede it with a backslash.
• A directory name may end in an '/'.
• For Unix and Win32, if a directory ends in two path separators "//", the backup file name will be built from the complete path to the file with all path separators changed to percent '%' signs. This will ensure file name uniqueness in the backup directory. On Win32, it is also possible to end with "\". However, When a separating comma is following, you must use "//", since "\" will include the comma in the file name. Therefore it is recommended to use '//', instead of '\'.
• Environment variables are expanded |:set_env|.
• Careful with '' characters, type one before a space, type two to get one in the option (see |option-backslash|), for example: > :set bdir=c:\tmp,\ dir\,with\,commas,\\ dir\ with\ spaces < - For backwards compatibility with Vim version 3.0 a '>' at the start of the option is removed. See also 'backup' and 'writebackup' options. If you want to hide your backup files on Unix, consider this value: > :set backupdir=./.backup,~/.backup,.,/tmp < You must create a ".backup" directory in each directory and in your home directory for this to work properly. The use of |:set+=| and |:set-=| is preferred when adding or removing directories from the list. This avoids problems when a future version uses another default. This option cannot be set from a |modeline| or in the |sandbox|, for security reasons.