Re: OT: about compressed tarball

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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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