Install ruby-oci8

gistfile1.txt

Step 1 
Go to oracle web site for some downloads http://www.oracle.com/technetwork/topics/intel-macsoft-096467.html.

Step 2
Download: instantclient-sqlplus, instantclient-sdk, instantclient-basic

Step 3
Create directories at /opt/oracle incase its not yet created with following command:
$ mkdir /opt/oracle

Step 4
Unzip instantclient-basic, move to /opt/oracle the unzipped folder will be something like instantclient_11_2.
Note : we will be moving other two unzipped folders in this folder, wont keep them separately.

Step 5
Next unzip instantclient-sqlplus move its filed & folders to /opt/oracle/instantclient_11_2/

Step 6 
Next unzip instantclient-sdk move its contents /opt/oracle/instantclient_11_2/

Step 7
Next, via terminal we will add some env variable. First, DYLD_LIBRARY_PATH=/opt/oracle/instantclient_11_2 export DYLD_LIBRARY_PATH

Secondly, ORACLE_HOME=/opt/oracle/instantclient_11_2 export ORACLE_HOME

Check if env variables are created properly by executing $ env

Step 8 
You may need to make a symbolic link.
  cd /opt/oracle/instantclient_11_2
  ln -s libclntsh.dylib.11.1 libclntsh.dylib

Step 9
Now run gem install ruby-oci8