I use this spec to make rpm and install ruby 1.9.3-p327 to CentOS 5.5 x86_64
Please remove all other ruby 1.8.x packages from your system (if you don't use rvm). Use rpm -qa | grep ^ruby to find old packages. Then run rpm -e for every package from the list you got.
Create rpm for ruby 1.9.3-p327
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-p327.tar.gz
cd ~/rpmbuild/SPECS
wget https://raw.github.com/AlexLapin/ruby-1.9.3-rpm/master/ruby19.spec
rpmbuild -bb ruby19.spec
And install it:
ARCH=`uname -m`
rpm -Uvh ~/rpmbuild/RPMS/${ARCH}/ruby-1.9.3p327-1.${ARCH}.rpm
Check ruby:
ruby -v
ruby 1.9.3p327 (2012-11-10 revision 37606) [x86_64-linux]
gem install rails