Keep Old Files
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`--keep-old-files'
`-k'
Do not replace existing files from archive. The
`--keep-old-files' (`-k') option prevents `tar' from replacing
existing files with files with the same name from the archive.
The `--keep-old-files' (`-k') option is meaningless with `--list'
(`-t'). Prevents `tar' from replacing files in the file system
during extraction.