(tar.info.gz) how to update

Info Catalog (tar.info.gz) update
 
 4.2.3.1 How to Update an Archive Using '--update'
 .................................................
 
 You must use file name arguments with the '--update' ('-u') operation.
 If you don't specify any files, 'tar' won't act on any files and won't
 tell you that it didn't do anything (which may end up confusing you).
 
    To see the '--update' option at work, create a new file, 'classical',
 in your practice directory, and some extra text to the file 'blues',
 using any text editor.  Then invoke 'tar' with the 'update' operation
 and the '--verbose' ('-v') option specified, using the names of all the
 files in the 'practice' directory as file name arguments:
 
      $ tar --update -v -f collection.tar blues folk rock classical
      blues
      classical
      $
 
 Because we have specified verbose mode, 'tar' prints out the names of
 the files it is working on, which in this case are the names of the
 files that needed to be updated.  If you run 'tar --list' and look at
 the archive, you will see 'blues' and 'classical' at its end.  There
 will be a total of two versions of the member 'blues'; the one at the
 end will be newer and larger, since you added text before updating it.
 
    The reason 'tar' does not overwrite the older file when updating it
 is because writing to the middle of a section of tape is a difficult
 process.  Tapes are not designed to go backward.   Media, for
 more information about tapes.
 
    '--update' ('-u') is not suitable for performing backups for two
 reasons: it does not change directory content entries, and it lengthens
 the archive every time it is used.  The GNU 'tar' options intended
 specifically for backups are more efficient.  If you need to run
 backups, please consult  Backups.
 
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