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(tar.info)compare

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Comparing Archive Members with the File System
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   The `--compare' (`-d'), or `--diff' operation compares specified
archive members against files with the same names, and then reports
differences in file size, mode, owner, modification date and contents.
You should _only_ specify archive member names, not file names.  If you
do not name any members, then `tar' will compare the entire archive.
If a file is represented in the archive but does not exist in the file
system, `tar' reports a difference.

   You have to specify the record size of the archive when modifying an
archive with a non-default record size.

   `tar' ignores files in the file system that do not have
corresponding members in the archive.

   The following example compares the archive members `rock', `blues'
and `funk' in the archive `bluesrock.tar' with files of the same name
in the file system.  (Note that there is no file, `funk'; `tar' will
report an error message.)

     $ tar --compare --file=bluesrock.tar rock blues funk
     rock
     blues
     tar: funk not found in archive

Depending on the system where you are running `tar' and the version you
are running, `tar' may have a different error message, such as:

     funk: does not exist

   The spirit behind the `--compare' (`--diff', `-d') option is to
check whether the archive represents the current state of files on
disk, more than validating the integrity of the archive media.  For
this later goal, Note: verify.