You cannot use SQL.SQLCODE as return code for Unix. Return codes for unix have to be <= 127.
But try this:
sqlplus -s <<EOF1
set serveroutput on feedback off verify off heading off echo off
whenever sqlerror exit 99;
if [ $? -ne 0 ]
#go on within the unix script
"The person who says it cannot be done should not interrupt the person doing it." --Chinese Proverb