While on a pentest where I needed access to the Oracle DB using sqlplus I found that the client wa present but not working, here are the steps to fix it
mv /usr/lib/oracle/* /usr/lib/
mv /usr/lib/oracle/* /usr/bin
wget ftp://fr2.rpmfind.net/linux/fedora/development/source/SRPMS/libaio-0.3.106-4.2.src.rpm
rpm2tgz libaio-0.3.106-4.2.src.rpm
tar xfz libaio-0.3.106-4.2.src.tgz
cd libaio-0.3.106-4.2
tar xvzf libaio-0.3.106.tar.gz
cd libaio-0.3.106
make prefix=/usr/local install
rm -rf libai*
I hope it helps

after this you can run sqlplus form the shell to connect to Oracle RDBMS Servers