I am adding some sources to an existing rpm .spec file by URL and don't have them downloaded yet. Is there a way to get rpmbuild to download the sources rather than doing it manually?
The spectool utility from the rpmdevtools package can do this. Just install rpmdevtools and point spectools at the .spec like so:
spectool -g -R SPECS/nginx.spec
It will download any missing sources into rpm's %{_sourcedir} (usually SOURCES) directory.