Set up Oracle environment in Red Hat Linux

Hi Experts,

I am attempting to set up environment for oracle 11202 on Redhat Linux 6.2 (64 Bit). I have installed oracle 11202. I have created  a db_setenv.sh file . The contents of this file are:

export ORACLE_HOME=/home/jan/app/jan/product/11.2.0/dbhome_1
export ORACLE_BASE=/home/jan/app/jan
export ORACLE_SID=april
export PATH=$ORACLE_HOME/bin:$PATH
export CLASSPATH=$ORACLE_HOME/jlib
export LIBPATH=$ORACLE_HOME/lib:$LIBPATH
sqlplus /nolog


I execute the above file by giging the comand ./db_setenv.sh and I get the SQL prompt as below:

[jan@localhost scripts]$ ./db_setenv.sh

SQL*Plus: Release 11.2.0.1.0 Production on Fri Apr 20 05:13:42 2012

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

SQL> conn /as sysdba
Connected.
SQL>
SQL>
SQL>

From here I am inside Oracle and that is good. The help I need is to modify my db_setenv.sh file in such a way that when I type cd $ORACLE_HOME it should take me to

home/jan/app/jan/product/11.2.0/dbhome_1

and when I type $ORACLE_BASE it should take me to:
/home/jan/app/jan