1. You need to first setup the environment variable for ORACLE_HOME in your Path. But if you don't know that then simply change the directory to the place where Oracle Database has been installed.

2. Use the following command to view the installed Oracle Homes and top level components:

opatch lshomes

RESULTS

Oracle Interim Patch Installer version 11.2.0.3.3

Copyright (c) 2012, Oracle Corporation.  All rights reserved.

Oracle Home       : /app/database/product/11.2.0/dbhome_1

Central Inventory : /home/fusion/oraInventory

   from           : /app/database/product/11.2.0/dbhome_1/oraInst.loc

OPatch version    : 11.2.0.3.3

OUI version       : 11.2.0.3.0

Log file location : /app/database/product/11.2.0/dbhome_1/cfgtoollogs/opatch/opatch2014-04-04_18-37-59PM_1.log