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From: rmtodd@uokmax.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: ARC/ZOO/TAR
Message-ID: <927@uokmax.UUCP>
Date: Thu, 3-Dec-87 14:18:02 EST
Article-I.D.: uokmax.927
Posted: Thu Dec  3 14:18:02 1987
Date-Received: Mon, 7-Dec-87 04:09:11 EST
References: <3027@umn-cs.cs.umn.edu> <8042@steinmetz.steinmetz.UUCP>
Reply-To: rmtodd@uokmax.UUCP ()
Distribution: na
Organization: University of Oklahoma, Norman, OK
Lines: 62

In article <8042@steinmetz.steinmetz.UUCP> davidsen@crdos1.UUCP (bill davidsen) writes:
>In article <3027@umn-cs.cs.umn.edu> amit@umn-cs.UUCP (Neta Amit) writes:
>tar doesn't save directories, as you said it creates them. You lose all
>info about owner, permissions, time modified, etc. It also *doesn't
>create empty directories!!* Many programs which keep status and restart
>info in directories will leave the directories empty when shut down.
  When run in the normal 'new (ANSI) format' mode, PD Tar does make entries
in the tar-file for the directories.  It saves their owner, permissions, time
modified.  If I remember correctly, the old (V7) tar format doesn't include
entries for directories, just for the files, and tar has to construct the
directories itself.  PD Tar, when reading new-format tarfiles, should create
the directories with appropriate mode and owner (if you're root).  It doesn't
handle mod times correctly (it creates the dir with the correct mod time, but
the mod time gets trashed when the files in the directory are extracted); John
Gilmore admits this is a bug which he hopes to fix in future releases.  
I don't see offhand why PD Tar would have any problem with empty directories;
if I get the chance I'll try it out this weekend and see.
  As a side note, the difference between the old and new tarfile format isn't
very great.  The only differences are that the new format has entries for
directories, and the new format headers have extra fields for the user and
group names, not just the uids.  Most standard tar programs should handle
PD Tar's output without problem, and vice versa.
>The "standard" tar doesn't compress, at least on V7, SysIII, SysV, or
>Ultrix. What you are proposing is (yet) another file format entirely.
>This is not a bad thing, but somewhat negates your earlier argument
>about standard. A regular (uncompressed) tar file will more widely
>readable than the compressed format.
The standard tar does not compress in and of itself;  it can produce 
compressed files if you do the appropriate pipe into compress.  You can
extract from a compressed tar-file just by
	zcat tarfile.Z | tar xvf -
The PDTar command
	tar xvfZ tarfile.Z 
just does the piping and executing of compress automatically.  Similarly, 
PDTar's
	tar cvfZ tarfile.Z dir
is equivalent to
	tar cvf - dir | compress >tarfile.Z
All you need to read compressed tarfiles on older systems is a copy of
compress.
>I'm not saying that your idea is without merit, and it should be
>considered as another alternative format. However, the question is not
>as clear as you believe. The advantage of archivers is that they allow
>easy random access to the files in an archive. The price of this is
>compressing them separately, which reduces the compression and increases
>the cpu needed. They allow easy replacement of individual files in the
>archive.
Well, tar allows random *access* to files in the archive; it just doesn't
allow random *updating* of the archive.  I can extract as few files as I want,
but if I change one file I have to rebuild the entire archive.  
>I will be evaluating pdtar in the next few weeks, and I expect it to be
>useful, and reliable (J.G. does good stuff). I don't expect it to be the
>only archiver I use, on UNIX, on PCs, and most of all on (yecch) VMS. At
>the moment zoo is the only thing I have which runs in all environments.
Zoo is awfully nice, and I use it a great deal myself.  Unfortunately, I also
do a great deal of work with MINIX, and ZOO just won't fit in the 64Kcode/
64Kdata space that MINIX allows.  PD Tar does.  (It also beats the living
daylights out of the tar that came with MINIX).
--------------------------------------------------------------------------
Richard Todd
USSnail:820 Annie Court,Norman OK 73069
UUCP: {allegra!cbosgd|ihnp4}!occrsh!uokmax!rmtodd