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