-@ignore
-The above is based on the following discussion:
-
- I have one question, or maybe it's a suggestion if there isn't a way
- to do it now. I would like to use @option{--gzip}, but I'd also like
- the output to be fed through a program like @acronym{GNU}
- @command{ecc} (actually, right now that's @samp{exactly} what I'd like
- to use :-)), basically adding ECC protection on top of compression.
- It seems as if this should be quite easy to do, but I can't work out
- exactly how to go about it. Of course, I can pipe the standard output
- of @command{tar} through @command{ecc}, but then I lose (though I
- haven't started using it yet, I confess) the ability to have
- @command{tar} use @command{rmt} for it's I/O (I think).
-
- I think the most straightforward thing would be to let me specify a
- general set of filters outboard of compression (preferably ordered,
- so the order can be automatically reversed on input operations, and
- with the options they require specifiable), but beggars shouldn't be
- choosers and anything you decide on would be fine with me.
-
- By the way, I like @command{ecc} but if (as the comments say) it can't
- deal with loss of block sync, I'm tempted to throw some time at adding
- that capability. Supposing I were to actually do such a thing and
- get it (apparently) working, do you accept contributed changes to
- utilities like that? (Leigh Clayton @file{loc@@soliton.com}, May 1995).
-
- Isn't that exactly the role of the
- @option{--use-compress-prog=@var{program}} option?
- I never tried it myself, but I suspect you may want to write a
- @var{prog} script or program able to filter stdin to stdout to
- way you want. It should recognize the @option{-d} option, for when
- extraction is needed rather than creation.
-
- It has been reported that if one writes compressed data (through the
- @option{--gzip} or @option{--compress} options) to a DLT and tries to use
- the DLT compression mode, the data will actually get bigger and one will
- end up with less space on the tape.
-@end ignore
-
-@node sparse
-@subsection Archiving Sparse Files
-@cindex Sparse Files
-@UNREVISED
-
-@table @option
-@opindex sparse
-@item -S
-@itemx --sparse
-Handle sparse files efficiently.
-@end table
-
-This option causes all files to be put in the archive to be tested for
-sparseness, and handled specially if they are. The @option{--sparse}
-(@option{-S}) option is useful when many @code{dbm} files, for example, are being
-backed up. Using this option dramatically decreases the amount of
-space needed to store such a file.
-
-In later versions, this option may be removed, and the testing and
-treatment of sparse files may be done automatically with any special
-@acronym{GNU} options. For now, it is an option needing to be specified on
-the command line with the creation or updating of an archive.
-
-Files in the file system occasionally have @dfn{holes}. A @dfn{hole} in a file
-is a section of the file's contents which was never written. The
-contents of a hole read as all zeros. On many operating systems,
-actual disk storage is not allocated for holes, but they are counted
-in the length of the file. If you archive such a file, @command{tar}
-could create an archive longer than the original. To have @command{tar}
-attempt to recognize the holes in a file, use @option{--sparse} (@option{-S}). When
-you use this option, then, for any file using less disk space than
-would be expected from its length, @command{tar} searches the file for
-consecutive stretches of zeros. It then records in the archive for
-the file where the consecutive stretches of zeros are, and only
-archives the ``real contents'' of the file. On extraction (using
-@option{--sparse} is not needed on extraction) any such
-files have holes created wherever the continuous stretches of zeros
-were found. Thus, if you use @option{--sparse}, @command{tar} archives
-won't take more space than the original.