Re: %{expand:...} documentation

[Jeff Johnson <n3npq jbj gmail com>]

On Aug 27, 2007, at 2:48 PM, Jos Vos wrote:

> On Mon, Aug 27, 2007 at 02:35:14PM -0400, Jeff Johnson wrote:
>
> > The macro primitive %{expand:...} is like eval in shell.
>
> That's what I thought...
>
> > > When browsing through spec files, I have the impression that it is
> > > unnecessarily used in a lot of cases.
> >
> > Likely.
>
> Just some excerpts from RHEL5 spec files (some are even used  
> frequently):
>
>  %{expand: %%define pyver %(python -c 'import  
> sys;print(sys.version[0:3])')}
>
>  %{expand: %%define build_with_freetype %{?_with_freetype:1}%{!? 
> _with_freetype:0}}

Ah, this is an optimization. The first pass of the %{expand: ...}  
invokes a helper
command, the 2nd pass does the define, so that the helper is not  
lazily executed
repeatedly.

> I think this is an example of proper use (as there is a recursion),  
> right?
>
>  %{expand: %%define _includedir %{_includedir}/%{name}}

In this case, it really doesn't matter how often "%{_includedir}/% 
{name}" is
expanded. Well, it _MAY_matter if the value of %{name} is changing,
but I doubt you can really solve the problem of, say, %{name} possibly  
changing
meaningfully by using %{expand:...}.

Invoking a helper repeatedly is what was being avoided by
using %{expand:...} in yr first example.

73 de Jeff