Re: [Bug-tar] 7z support for GNU tar

[Doug McLaren]

On Mon, Oct 31, 2005 at 12:27:44PM +0100, Rene Leonhardt wrote:

| I am wondering if there are any plans to support the LGPL 7-Zip compression
| format besides the already supported compress, gzip and bzip2 formats.

7z isn't very popular (yet?) in the *nix communities, and these are
the people who mostly use tar.  There's not much overlap.

Also, 7z is more like zip or rar, which are an archiver plus a
compresser, where gzip, bzip2 and compress are just stream compressers
-- they compress a single stream.  So it doesn't really make that much
sense to use 7z with tar, because 7z already has the ability to
combine many files into one compressed archive, so tar isn't needed.

(The only thing that tar would really add to the equation is the
ability to better preserve things like permissions, links,
atime/mtime/ctime, etc.)

gnu tar does have the ability to use any compression program that
accepts a stream on stdin and emits the compressed stream on stdout
and vice versa, as long as the decompression is turned on with the -d
flag.  (This is enabled in gnu tar with the
--use-compress-program=whatever flag.)  So if 7z supported this, it
could work right now.

Looking at p7zip, which is the *nix port of p7, it doesn't looke like
it quite supports this.

Note that the instructions on p7zip do tell how to use it with tar --

   Backup and limitations
       DO NOT USE the 7-zip format for backup purpose on Linux/Unix because :
        - 7-zip does not store the owner/group of the file.

       On Linux/Unix, in order to backup directories you must use tar :
        -  to  backup  a  directory   :  tar cf - directory |
           7za a -si directory.tar.7z
        - to restore your backup : 7za x -so directory.tar.7z | tar xf -

Which is almost what gnu tar needs, but it appears that it must have
an archive name on the command line, so it can't be made to work with
gnu tar the way you want it to.

-- 
Doug McLaren, address@hidden
She walked into my office like a centipede with 98 missing legs.