OT: about compressed tarball
Stephen Liu
satimis at yahoo.com
Sun Jun 25 00:28:45 UTC 2006
Hi James,
Tks for your advice.
I made following test;
1) re-created another compressed tarball on the old directory, old-AAA
$ tar -jcpf AAA.tar.bz2 old-dirA/
2) used following command line to create a new compressed tarball
$ bunzip2 AAA.tar.bz2 ; tar -upf AAA.tar /home/path/to/new-dirA ; bzip2
AAA.tar
The new compressed tarball created consisted of the old and new
directories, without removing the old directory.
I think tar and bzip2 are not the tools for my application. Any other
suggestions? TIA
B.R.
SL
> Stephen Liu wrote:
> > I create a tarred file then compressed with bzip with following
> command
> > line;
> >
> > # tar -jcpf AAA.bz2 /home/path/to/dirA
> >
> > dirA is about 2G in size.
> >
> > After working several days on dirA I want to create a new
> compressed
> > tarred file. Instead of repeating the above command, is there a way
> > starting from the old file AAA.bz2 making use of the options -u,
> -N,
> > -G, etc. to reduce the compressing time? I looked around on man tar
> and
> > Internet and could not sort out their combination on the command
> line.
>
> You wouldn't be able to do this with command lines. bzip2 compresses
> 900K [1] blocks at a time: it might be possible, if a 900K block
> hasn't
> changed, to "carry it forward" from the earlier .tar.bz2 to the next,
> but you'd need to write a program that got pretty deep into the .tar
> and
> .bz2 format. [2]
>
> If you really want faster compression, possibly at the expense of
> file-size, then gzip might be a much better answer for you. It
> doesn't
> compress as well, but it can compress a lot faster. (Quite how much
> faster depends on your processor architecture).
>
> Hope this helps,
>
> James.
>
> [1] By default: see man bzip2 for details.
> [2] Someone's going to quibble if I don't quote the bzip2 man page
> saying
> bzip2 compresses files in blocks, usually 900kbytes long.
> Each block
> is handled independently. If a media or transmission error
> causes a
> multi-block .bz2 file to become damaged, it may be possible to
> recover
> data from the undamaged blocks in the file.
> --
> E-mail address: james | Whenever [Richard I] returned to England he
> always
> @westexe.demon.co.uk | set out again immediately for the
> Mediterranean and
> | was therefore known as Richard Gare de Lyon.
> | -- '1066 and All That'
>
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