ORA_DB variable in Oracle startup script
See below:
#! /bin/sh -x
#
# Change the value of ORACLE_HOME to specify the correct Oracle home
# directory for your installation.
ORACLE_HOME=/u01/app/oracle/product/11.2.0/dbhome_1
#
# Change the value of ORACLE to the login name of the
# oracle owner at your site.
#
ORACLE=oracle