Re: BuildRequires: how vary depending on build host?

[Nick Urbanik <nicku vtc edu hk>]

Thank you very much Tim, for the great background on RPM macros.  The shell
programming is no problem; the main problem was my lack of understanding of
RPM.  Thank you for your most helpful insight.  Your examples are very helpful.

Tim Mooney wrote:

> In regard to: BuildRequires: how vary depending on build host?, Nick...:
>
> >Dear Folks,
> >
> >I am writing RPM packages.  How do I write a BuildRequires statement
> >that depends on the version of Red Hat/Fedora of the build host?
> >
> >My problem is that the package needs db3-devel on build platforms Red
> >Hat 7.3 and older, and needs db4-devel otherwise.  Please could anyone
> >suggest a macro or some sensible way of writing such a BuildRequires
> >statement?  I would be most grateful for any suggestions.
>
> Disclaimer: I'm behind the times with RPM (but I do follow the list pretty
> closely and look longingly at *some* of the features in recent RPM.  ;-) )
>
> Before you can make the determination in a spec file, you need to be able
> to make the determination programmatically.  If you were going to make
> the determination of "older than 7.3" from a shell script, how would you
> do it?
>
> For better or worse, when I've had to do this, I generally look for
> /etc/redhat-release, and pull out the version from that.  Enterprise Linux
> makes it a little harder because you can't just do something like:
>
>         vers=`awk '{ print $5 }' /etc/redhat-release`
>         # can't use expr, it doesn't like floats
>         vers_x_10=`/bin/echo -e "$vers\n10\n*\np\n" | dc | sed -e 's/.0$//'`
>         if test $vers_x_10 -le 73 ; then
>                 # whew, what smells?
>                 :
>         else
>                 # that's the stuff
>                 :
>         fi
>
> You have to also check if it's Enterprise, and then Enterprise 2.1 would
> be "older than 7.3" but Enterprise 3.0 is not.  Note that the version
> field also isn't in position 5 in the file in that case either.
>
> If you know all the codenames for the versions of Red Hat of vintage 7.3
> and older, it's probably more straightforward to egrep for all of them.
> If grep finds a match, it's "7.3 or older".
>
> Once you have a programmatic way of determining the question, that can be
> turned into a macro:
>
> %define is_rh_lt_73     %(your shell code here)
>
> You basically want your shell code to *output* `1' if it is RH <= 7.3, and
> 0 if it's not.  The trick is going to be cramming all your shell code into
> the RHS of that macro.  ;-)
>
> And then you can do something like (my syntax may be a bit off)
>
> %if %{is_rh_lt_73}
> BuildRequires: db3-devel
> %endif
>
> %if %{!is_rh_lt_73}
> BuildRequires: db4-devel
> %endif
>
> You can learn a lot by looking at /usr/share/doc/rpm/macros and reading
> some of the /usr/lib/rpm/macros that are part of RPM.
>
> If it's any consolation, it's not an easy problem.  Getting a succinct bit
> of shell code that answers 0 or 1 is the hard part, and then stuffing that
> shell code into %(...) for evaluation is not going to be trivial
> either, but once you've solved *those* two problems, the rest is pretty
> trivial.  ;-)

--
Nick Urbanik   RHCE                               nicku(at)vtc.edu.hk
Dept. of Information & Communications Technology
Hong Kong Institute of Vocational Education (Tsing Yi)
Tel:   (852) 2436 8576, (852) 2436 8713          Fax: (852) 2436 8526
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