Ruby 1.9.3-p0 makes psych—the replacement for 1.8.7’s YAML library, Syck—the default YAML parser. Psych is a wrapper around libyaml, so you’re going to need it installed and configured before installing Ruby.

If you install 1.9.3-p0 without libyaml, you’ll see warnings like this:

It seems your ruby installation is missing psych (for YAML output). To eliminate this warning, please install libyaml and reinstall your ruby.

Installing libyaml

$ wget http://pyyaml.org/download/libyaml/yaml-0.1.4.tar.gz
$ tar xzvf yaml-0.1.4.tar.gz
$ cd yaml-0.1.4
$ ./configure --prefix=/usr/local
$ make
$ make install

Quick review of what’s going on: download and untar the source code, change to the directory and install the package. You may need to sudo the make install command. Your mileage may vary.

Installing Ruby 1.9.3-p0

$ wget http://ftp.ruby-lang.org/pub/ruby/1.9/ruby-1.9.3-p0.tar.gz
$ tar xzvf ruby-1.9.3-p0.tar.gz
$ cd ruby-1.9.3-p0
$ ./configure --prefix=/usr/local --enable-shared --disable-install-doc --with-opt-dir=/usr/local/lib
$ make
$ make install

After installing, you can verify that Ruby was installed with ruby -v. It’s also worth trying gem --version to make sure you don’t get any errors regarding psych.

I tried installing libyaml-devel and libyaml from Yum, but couldn’t get ruby installed and recognizing those packages. Out of frustration, I turned to installing libyaml by source and it Just Worked™