create or replace
function test_fn
RETURN varchar2
IS
test_date VARCHAR2(100);
BEGIN

select to_char(sysdate,'DD-MON-YY') into test_date from dual;   
return test_date ;
END test_fn;

$ ./calltest_fn.ksh
var test_var:=test_fn1; calltest_fn.ksh file1 file2 file3 ERROR at line 4: ORA-06550: line 4, column 11: PLS-00201: identifier 'test_fn1' must be declared ORA-06550: line 4, column 1: PL/SQL: Statement ignored

$ uname -a
Linux <machine name> 2.6.9-89.ELsmp ####################

#!/usr/bin/ksh

#set -x

var=`sqlplus -s <<EOF
user/pass@DB
WHENEVER SQLERROR EXIT FAILURE
WHENEVER OSERROR  EXIT FAILURE
set serveroutput on
set feedback off
set linesize 250
DECLARE
test_var varchar2(100);
BEGIN
test_var:=test_fn1;
dbms_output.put_line(test_var);
END;
/
quit;
EOF`

echo var $var