Currently I have responsibilities for Fedora. I want to set ones up for Oracle EL and CentOS

How do I see what yum will set the $distribution/$releasever/$basearch variables too? Is there a way to check?

$releasever will be the release number of your Fedora install. That is, if you're running Fedora 8, $releasever=8. If you're running Fedora Core 5, $releasever=5.
$basearch can be determined by running "uname -i"
$distribution will be "fedora-release" (not 100% sure about that one, none of my repository configs use it.)

$releasever is actually one of these:
rpm -q --queryformat '%{VERSION}' redhat-release
rpm -q --queryformat '%{VERSION}' fedora-release
rpm -q --queryformat '%{VERSION}' centos-release

Sorry I guess I wasn't that clear on my question.

My question isn't where it get's the info...I just wanted to see what all the environment variables are set to on a distro so I can use it to check distros like OEL5, CentOS 5, etc.

$releasever is not setup on bash prompt so I wanted to know if I could drive yum to set them up for me on the fly.

NOT Always...

I have a system where it is "7Server" but the above does not give me that.

This seems to work universally for fedora, centos and redhat systems, both older "yum" only and newer "dnf" systems... But it is a little slow.

yum-debug-dump --norepos /dev/stdout | grep -oP '^ releasever:\s*\K\S+'