tar: backup
1
1 4.5 Backup options
1 ==================
1
1 GNU 'tar' offers options for making backups of files before writing new
1 versions. These options control the details of these backups. They may
1 apply to the archive itself before it is created or rewritten, as well
1 as individual extracted members. Other GNU programs ('cp', 'install',
1 'ln', and 'mv', for example) offer similar options.
1
1 Backup options may prove unexpectedly useful when extracting archives
1 containing many members having identical name, or when extracting
1 archives on systems having file name limitations, making different
1 members appear as having similar names through the side-effect of name
1 truncation.
1
1 When any existing file is backed up before being overwritten by
1 extraction, then clashing files are automatically be renamed to be
1 unique, and the true name is kept for only the last file of a series of
1 clashing files. By using verbose mode, users may track exactly what
1 happens.
1
1 At the detail level, some decisions are still experimental, and may
1 change in the future, we are waiting comments from our users. So,
1 please do not learn to depend blindly on the details of the backup
1 features. For example, currently, directories themselves are never
1 renamed through using these options, so, extracting a file over a
1 directory still has good chances to fail. Also, backup options apply to
1 created archives, not only to extracted members. For created archives,
1 backups will not be attempted when the archive is a block or character
1 device, or when it refers to a remote file.
1
1 For the sake of simplicity and efficiency, backups are made by
1 renaming old files prior to creation or extraction, and not by copying.
1 The original name is restored if the file creation fails. If a failure
1 occurs after a partial extraction of a file, both the backup and the
1 partially extracted file are kept.
1
1 '--backup[=METHOD]'
1 Back up files that are about to be overwritten or removed. Without
1 this option, the original versions are destroyed.
1
1 Use METHOD to determine the type of backups made. If METHOD is not
1 specified, use the value of the 'VERSION_CONTROL' environment
1 variable. And if 'VERSION_CONTROL' is not set, use the 'existing'
1 method.
1
1 This option corresponds to the Emacs variable 'version-control';
1 the same values for METHOD are accepted as in Emacs. This option
1 also allows more descriptive names. The valid METHODs are:
1
1 't'
1 'numbered'
1 Always make numbered backups.
1
1 'nil'
1 'existing'
1 Make numbered backups of files that already have them, simple
1 backups of the others.
1
1 'never'
1 'simple'
1 Always make simple backups.
1
1 '--suffix=SUFFIX'
1 Append SUFFIX to each backup file made with '--backup'. If this
1 option is not specified, the value of the 'SIMPLE_BACKUP_SUFFIX'
1 environment variable is used. And if 'SIMPLE_BACKUP_SUFFIX' is not
1 set, the default is '~', just as in Emacs.
1