Find out what repo an rpm was installed from

gistfile1.txt

yum-utils provides repoquery

For a single package, you can find this with

repoquery -i package

PACKAGE=ruby-enterprise
repoquery --qf "%{repoid}" $PACKAGE
Replace $PACKAGE with the name of the package you care about.

You can find all packages that came from a specific repository with

REPO=ruby-enterprise-opt
repoquery --repoid=$REPO -a --qf "%{name}" | sort > repo_packages
rpm -qa --qf "%{name}\n" | sort > installed_packages
comm -1 -2 repo_packages installed_packages
Replace $REPO with the id of the repository you care about; you can see the ids of all your enabled repositories with yum repolist.