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[Help-tar] Compression Methods

From: Yannick Gingras
Subject: [Help-tar] Compression Methods
Date: Tue, 31 Oct 2006 11:49:42 -0500
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.51 (gnu/linux)

On GNU/Linux and on other Posix systems, the usual way to serialize a
branch of the file system tree is to make a "tarball".  Those tarballs
are used to distribute programs and other packages but since I'm
posting to help-tar you probably all know that.

Tar handle the serialization and let another program take care of the
compression.  This is very good and two popular such programs are gzip
and bzip2.  Since most tarballs are distributed compressed, GNU tar
support command line arguments to trigger the invocation of the
(un)compression system.  

The command line interface uses different command line options for
different compression systems.  This makes a lot of sense if you are
creating a tarball: you can decide how you want to compress it; you
may go for bzip2 to get a better compression ratio at the cost of more
runtime or you may choose gzip to minimize CPU work.

But for tarball extraction, it makes little sense to require the user
to specify the compression algorithm since it can be safely inferred
from the tarball meta-data.  For this reason, I'm looking for a
command line option to GNU tar that would just invoke the right
decompression system.

Is such option already in there?

If so, I'm sorry for this message and I will RTFM ASAP.  I'd like to
point out though that I did RTFM and that if such option exists it
might benefit from cross reference in the texinfo sections mentioning
-x and -j

If not such option exists, I would like to know if there is something
that prevents its implementation.  I understand that GNU tar does more
than just tarball management and that when working on streams,
inspection of the meta-data might not be an option.  

I could write myself wrapper script and I would be done by the time it
took me to write this email but I feel that I would help more users if
I implement this option right into GNU tar.


Yannick Gingras

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