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(tar.info)Dealing with Old Files

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Options Controlling the Overwriting of Existing Files
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   When extracting files, if `tar' discovers that the extracted file
already exists, it normally replaces the file by removing it before
extracting it, to prevent confusion in the presence of hard or symbolic
links.  (If the existing file is a symbolic link, it is removed, not
followed.)  However, if a directory cannot be removed because it is
nonempty, `tar' neither removes it nor modifies its ownership,
permissions, or time stamps.

   To be more cautious and prevent existing files from being replaced,
use the `--keep-old-files' (`-k') option.  It causes `tar' to refuse to
replace or update a file that already exists, i.e., a file with the
same name as an archive member prevents extraction of that archive
member.  Instead, it reports an error.

   To be more aggressive about altering existing files, use the
`--overwrite' option.  It causes `tar' to overwrite existing files and
to follow existing symbolic links when extracting.  The
`--overwrite-dir' option is somewhat more conservative than
`--overwrite': it overwrites metadata (ownership, permission, etc.) for
directories, but removes other files before extracting them.

   Some people argue that GNU `tar' should not hesitate to overwrite
files with other files when extracting.  When extracting a `tar'
archive, they expect to see a faithful copy of the state of the
filesystem when the archive was created.  It is debatable that this
would always be a proper behavior.  For example, suppose one has an
archive in which `usr/local' is a link to `usr/local2'.  Since then,
maybe the site removed the link and renamed the whole hierarchy from
`/usr/local2' to `/usr/local'.  Such things happen all the time.  I
guess it would not be welcome at all that GNU `tar' removes the whole
hierarchy just to make room for the link to be reinstated (unless it
_also_ simultaneously restores the full `/usr/local2', of course!  GNU
`tar' is indeed able to remove a whole hierarchy to reestablish a
symbolic link, for example, but _only if_ `--recursive-unlink' is
specified to allow this behavior.  In any case, single files are
silently removed.

   Finally, the `--unlink-first' (`-U') option can improve performance
in some cases by causing `tar' to remove files unconditionally before
extracting them.