Re: 'tar' in the GNU Coding Standards

[Dr. David Kirkby]

Ralf Wildenhues wrote:
> Hello David,
>
> sorry about the delay.
>
> * Dr. David Kirkby wrote on Sat, Oct 24, 2009 at 04:35:36PM CEST:
> > ----------------------------------------------------------
> > The configure script and the Makefile rules for building and
> > installation should not use any utilities directly except these:
> >
> >      awk cat cmp cp diff echo egrep expr false grep install-info
> >      ln ls mkdir mv pwd rm rmdir sed sleep sort tar test touch tr true
> >
> > ----------------------------------------------------------
>
> > I believe 'tar' should removed from that list, but allow someone to
> > select a variable for 'tar'. On Solaris for instance, Sun's tar can
> > not extract all tar files programs written with GNU tar, though it
> > does manage most of them. (It's not simply the fact some options
> > just as z and j are not supported, but more fundamental issues.
>
> I agree that there are problems with non-portable tarballs.  That brings
> up a couple of points:

The best way IMHO would be for GNU tar to default to a more portable format 
rather than its own 'standard'.

Reading http://www.gnu.org/software/automake/manual/tar/Formats.html

it implies this will happen. The sooner the better I feel. I do not know how 
well Sun's tar will handle the tar format of GNU tar then.


> The typical user downloading a tarball from the net and extracting it
> does not use the $(TAR) in the makefile inside the tarball; he uses tar
> on the command line, before the makefile is used for the first time, and
> he doesn't need `make dist' or similar which would use tar again from
> within the makefile.

> If tar is not sufficient to extract some package tarball, then this
> ought to be clear from the installation instructions.  However,
> requiring, say, GNU tar in general, would be quite some move; we don't
> usually any other GNU tools to be preinstalled, if only for
> bootstrapping reasons.

A much easier move would be to get GNU tar to write by default in a more 
portable format.

I know there is one package in the Sage project which will not extract with 
Sun's tar. But if one uses Sun's tar to create the tarball, GNU tar can extract 
it ok.

> The 'Releases' node of the GCS describes some of the precautions to use
> when creating package tarballs.  If possible, I think it would be
> prudent to advise the tarball creator to use the most portable archive
> format possible.  The GNU tar manual has `Portability' and `Formats'
> sections about this, and the GNU Automake manual node `Options' shows
> how to apply them to your package, should you use automake.  Automake
> uses old v7 archive format by default for `make dist'.

That sounds sensible. I'm not sure why GNU tar does not default to something 
sensible like that.

> I'm unsure of how wide-spread installation of a more capable tar program
> is on systems with a limited vendor tar.



> > Issues with non-GNU versions of tar are common on lots of non-linux
> > platforms when using GNU tools.
> >
> > hence it's better the user was able to write:
> >
> > $ TAR=/usr/local/bin/gtar
> > $ export TAR
>
> How would you set $(TAR) if not supplied by the user though? 

I'm not a wizard on Makefiles, but is it not possible to write them in such a 
way that if the environment variable 'TAR' is unset, then $TAR gets set to 
'tar', otherwise it is whatever the TAR is set to?

> I haven't
> yet seen a good Autoconf test for a capable tar, besides one that
> wouldn't select GNU tar only; writing such a macro would probably be a
> good thing to do before changing GCS.  Requiring the user to select a
> tar program manually seems a bit awkward.  Note that one alternative to
> choosing a tar program is to use something like the `missing' program
> that Automake selects for some tools that may not be present.  OTOH I
> don't see how packages can ignore or replace tar's functionality in that
> case, unlike, say, makeinfo, where the info files are typically
> distributed in the tarball.

Jöerg Schilling's 'star' is one other implementation I am aware of. He seems to 
have the knack of writing extremely portable code.

> BTW, I agree that egrep and fgrep should be fixed, as you noted
> somewhere in this thread.

Can you personally do something about the fgrep and egrep? Or do you know who to 
handle the issue to?

> Thanks,
> Ralf

Dave