Zlib

require "zlib" # => false ?!

If you have issues with zlib not being available in ruby / irb please try the following configure option:

∴ rvm package install zlib
∴ rvm remove 1.9.1
∴ rvm install 1.9.1 -C --with-zlib-dir=$HOME/.rvm/usr

Where you replace '/usr/local' with the prefix where your zlib packages are.

If you simply cannot seem to get this to work you can have RVM install a copy of zlib into ~/.rvm/usr like so:

∴ rvm package install zlib
∴ rvm remove 1.9.1
∴ rvm install 1.9.1