yum install -y rpm-build rpmdevtools
rpmdev-setuptree
cd ~/rpmbuild/SOURCES
wget http://ftp.ruby-lang.org/pub/ruby/1.9/ruby-1.9.3-p194.tar.gz
cd ~/rpmbuild/SPECS
curl https://raw.github.com/kamaradclimber/ruby-1.9.3-rpm/master/ruby19.spec > ruby19.spec
rpmbuild -bb ruby19.spec
rpm -Uvh ~/rpmbuild/RPMS/x86_64/ruby-1.9.3p194-1.el6.x86_64.rpm

PROFIT!

• Builds
• Installs
• Overwrites/upgrades your currently installed ruby package (DANGEROUS)

• Split packages into ruby-libs, ruby-devel, etc (looking for help here)
• Install alongside Ruby 1.8.x

Tested working (as sane as I could test for) on:

• CentOS 6.1 x86_64
• CentOS 6.2 i686
• CentOS 5.7 x86_64

This should on RHEL, though. Let me know if it doesn't.

• Working off from https://github.com/imeyer/ruby-1.9.2-rpm. Usual disclaimers apply.
• If you need YAML support, you will need to have libyaml installed. If you like to build your own, you can use my spec at https://github.com/rilindo/rpms/tree/master/specs/libyaml. In the future, I'll add that as a requirement.
• libffi also needs to be installed if you need Ruby-FFI. I will add that is a require in a future update.