Ruby-OCI8 1.0.2 gem available, a big thanks to Kubo. I’m glad to have proposed this and made a little contribution.
To install Ruby-OCI8 via gem, follow these steps:
- su – root
- rpm -ivh oracle-instantclient-basic-11.1.0.1-1.rpm oracle-instantclient-devel-11.1.0.1-1.rpm (download link; or install oracle full client)
- export LD_LIBRARY_PATH=/usr/lib/oracle/11.1.0.1/client/lib:$LD_LIBRARY_PATH
- cd /usr/lib/oracle/11.1.0.1/client/lib
- ln -s libclntsh.so.11.1 libclntsh.so
- gem install ruby-oci8
In one word, If you’ve set up oracle db stuff and LD_LIBRARY_PATH well, simply run:
$ sudo gem install ruby-oci8
or
$ sudo gem update ruby-oci8 (for update)
No “download ruby-oci8.tgz and ruby setup.rb” any more 
Enjoy!
how shall i on Windows
On Windows:
1. download Oracle Database Instant Client http://www.oracle.com/technology/tech/oci/instantclient/index.html
2. set LD_LIBRARY_PATH accordingly
3. C:\> gem install ruby-oci8