dynamic dependency check

[Dhanvi K <dhanvik gmx net>]

Hi,
 
    I would like my spec file to dynamically pick up rpm requirements 
depending on the OS on which the RPM is being installed. for e.g. If the 
RPM is being installed on Fedora box, then the spec should pick up one 
set of dependency rpms, while if its installing on a RedHat Enterprise 
box,  then it should pick up another set of RPMS. 

    I would like to know whether and how this is possible in the spec 
file ? Thanks for your time and advice

Regards,
Dhanvi.