Check whether a macro is undefined or has a specific value

[Daniel Neuberger]

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

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?

- Daniel