From Fedora Project Wiki
Purpose: There are some additional macros for DistTag that make it much easier to conditionalize inside of spec files.
Specifically, I propose that the following helper macros be added and the DistTag documentation updated accordingly:
%{?fedora: %{expand: %%define fc%{fedora} 1}} %{?rhel: %{expand: %%define el%{rhel} 1}}
This means that if %{fedora} is set to 7, the following macro is set:
%define fc7 1
This permits easier conditionalization in spec files. For example, with these defines, you can do:
%{?el5: a} %{?el4: b} %{?el3: c} %{?el2: d}
Without these macros, you have to resort to:
%if "%rhel" == "5" a %endif %if "%rhel" == "4" b %endif %if "%rhel" == "3" c %endif %if "%rhel" == "2" d %endif