Check whether a macro is undefined or has a specific value

[James Antill]

On Thu, 2011-08-18 at 10:12 +0200, Marco wrote:
> 2011/8/17 Daniel Neuberger <daniel.neuberger at gmail.com>:
> > On 08/16/2011 12:26 PM, Marco wrote:
> >>
> >> Thanks. I don't need to define another macro based on the value of
> >> %{__foo}. However based on your suggestion, I think I can do this,
> >> which seems to work:
> >>
> >> %if %{?__foo:1}%{!?__foo:0}
> >> %if "%{__foo}" == "1"
> >>   echo "foo is defined and is 1"
> >> %else
> >>   echo "foo is defined, but has some other value: %{__foo}"
> >> %endif
> >> %else
> >>   echo "foo is not defined"
> >> %endif
> >>
> >> Does this look correct/reliable enough or is there a better way to do
> >> what I'm trying to do? Thanks.
> >
> > I've never found documentation with the specifics of the %if macro, so
> > testing to see what works is the best method I know.  It seems like the
> > above works.  If you all need "do something" and "skip" block, the below is
> > less verbose:
> >
> > %if "%{?__foo:%{__foo}}%{!?__foo:0}" == "1"
> >  echo "foo is defined and is 1"
> > %else
> >  echo "foo is not defined or not equal to 1"
> > %endif
> 
> Ah thanks, I hadn't thought of this.
> 
> > Alternatively, you could also define a macro that expands to the "do
> > something" when needed, and expands to nothing otherwise.  I don't know of
> > simpler way to check equality though (but I'm kind of new to this stuff
> > too).
> >
> > Out of curiosity (if you don't mind me asking), why do you need to check
> > both for definition and equality?  What are you trying to do?
> 
> Sure. It's just that rpmbuild will be called from people's makefile,
> where they are supposed to run it by doing rpmbuild ... --define
> '__foo 1' if they want some special functionality to be enabled, and
> define it to 0 if not. Despite having been told this, I'm 100% sure
> that what will happen is that some people will define it correctly,
> some will do --define '__foo 0', some will not bother defining it (or
> will plain forget), possibly others will do yet other variations
> (typos, --define '__foo TRUE' or whatever),

 If you just have a boolean, why not use:

http://rpm.org/wiki/PackagerDocs/ConditionalBuilds

...instead?