My script code as follows
--------------------------------------------
. database_checking.sh

echo "Database Name" $db_name
echo "set feed off verify off pagesize 0
select username from user_users;"|sqlplus -s /@$db_name|read user_name
---------------------------------------------------------------

My database_checking.sh code follows which return db_name variable to above code....which is furthur used for retrieving username ...
-----------Start------------------------------------------------
db_var=1
while test $db_var -eq 1
do
echo "\n\t\t\tEnter Database Name"
echo "\t\t\t[ Example:marketbld.uk.d.ch ] or Press [ 'Q'/'q'] to exit :\c"
read db_name
func_meta_ch "$db_name"

if [ "!$db_name!" != "!!" -a $var_meta_ch -eq 0 ]
then
expr $db_name + 2 >/dev/null 2>&1
db_val=$?

if [ $db_val -ne 0 ]
then
echo "set feed off verify off pagesize 0
select count(1) from mktactivity;"|sqlplus -s /@$db_name|read sqldb_name

expr $sqldb_name + 2 >/dev/null 2>&1
db_cnt=$?

if [ "!$sqldb_name!" = "!ERROR:!" ]
then
echo "\t\t\tError: Database name entered does not exist."
else
if [ $db_cnt -ne 0 ]
then
echo "\t\t\tError: Database name entered does not exist."
else
db_var=2
fi
fi
else
echo "\t\t\tError: Database name entered does not exist."
fi
else
echo "\t\t\tError: Invalid Database name."
fi
done
echo $db_name

------------End ------------------