In CentOS, default Ruby version is 1.8.7.

I wrote a chef cookbook that lets you install version 1.9.3 via compiling source or using rvm.

cookbook is here:

https://github.com/chokkoyamada/chef-repo/tree/master/cookbooks/ruby/recipes

1) From source:

script "install_libyaml" do
  interpreter "bash"
  user "root"
  cwd "/usr/local/src/"
  code <<-EOH
  wget http://pyyaml.org/download/libyaml/yaml-0.1.4.tar.gz
  tar zxvf yaml-0.1.4.tar.gz
  cd yaml-0.1.4
  ./configure --prefix=/usr/local
  make
  make install
  EOH
end

script "install_ruby" do
  interpreter "bash"
  user "root"
  cwd "/usr/local/src/"
  code <<-EOH
  wget ftp://ftp.ruby-lang.org/pub/ruby/1.9/ruby-1.9.3-p125.tar.gz
  tar zxvf ruby-1.9.3-p125.tar.gz
  cd ruby-1.9.3-p125
  ./configure --prefix=/usr/local --enable-shared --disable-install-doc --with-opt-dir=/usr/local/lib
  make
  make install
  EOH
end

2) via RVM

package "git" do
  action :install
end

script "install_rvm" do
  not_if "rubytest=`ruby -e 'puts RUBY_VERSION' | grep '1.9.3'`; echo $?"
  interpreter "bash"
  user "root"
  cwd "/usr/local/src/"
  code <<-EOH
  curl -L https://get.rvm.io | bash -s stable
  source "/usr/local/rvm/scripts/rvm"
  command rvm install 1.9.3
  rvm use 1.9.3 --default
  EOH
end

Reference:

RVM: Ruby Version Manager - Installing RVM

https://rvm.io/rvm/install/

CentOSにRails 3.2.xとruby 1.9.3-p125をインストールする方法 - memo.yomukaku.net

http://memo.yomukaku.net/entries/KzbT3fR