sqlplus: error while loading shared libraries: libsqlplus.so wrong ELF class

sqlplus: error while loading shared libraries: libsqlplus.so wrong ELF class 

This error happens If you are working on a 64 bit operating system and pointing to a 32 bit library.

So this is how your environment variables should look like.

PATH=$PATH:$HOME/bin
ORACLE_HOME=/x/home/oracle/product/11.2.0.1
PATH=$ORACLE_HOME/bin:$PATH
PATH=$ORACLE_HOME/lib64:$PATH
LD_LIBRARY_PATH=$ORACLE_HOME/lib64
export ORACLE_HOME
export LD_LIBRARY_PATH
export PATH 

This will fix the issue.

How to find whether ORACLE is installed on your linux box

I was wondering how to find whether oracle was installed on my office box. I found an easy way of doing it.

vi /etc/oratab 

You can find the installation directory of the oracle instance here.