$
$
$ cat -n test_function.sh
     1  #!/usr/bin/bash
     2  var=`sqlplus -s test/test <<EndOfLine
     3  WHENEVER SQLERROR EXIT FAILURE
     4  WHENEVER OSERROR  EXIT FAILURE
     5  set serveroutput on
     6  set echo off
     7  set feedback off
     8  set verify off
     9  set linesize 500
    10  DECLARE
    11  test_var varchar2(100);
    12  BEGIN
    13  test_var:=test_fn(test_var);
    14  dbms_output.put_line(test_var);
    15  END;
    16  /
    17  quit;
    18  EndOfLine`
    19  echo "RETURN VALUE = $?"
    20  echo "VALUE OF VAR = $var"
    21
$
$ ./test_function.sh
RETURN VALUE = 0
VALUE OF VAR = 14-MAY-10
$
$

$
$
$ cat -n test_function.sh
     1  #!/usr/bin/bash
     2  var=`sqlplus -s test/test <<EndOfLine
     3  WHENEVER SQLERROR EXIT FAILURE
     4  WHENEVER OSERROR  EXIT FAILURE
     5  set serveroutput on
     6  set echo off
     7  set feedback off
     8  set verify off
     9  set linesize 500
    10  DECLARE
    11  test_var varchar2(100);
    12  BEGIN
    13  test_var:=fn_test(test_var);
    14  dbms_output.put_line(test_var);
    15  END;
    16  /
    17  quit;
    18  EndOfLine`
    19  echo "RETURN VALUE = $?"
    20  echo "VALUE OF VAR = $var"
    21
$
$ ./test_function.sh
RETURN VALUE = 1
VALUE OF VAR = test_var:=fn_test(test_var);
          *
ERROR at line 4:
ORA-06550: line 4, column 11:
PLS-00201: identifier 'FN_TEST' must be declared
ORA-06550: line 4, column 1:
PL/SQL: Statement ignored

$
$

test@ORA11G>
test@ORA11G> -- check my function code
test@ORA11G> select text from user_source where name = 'TEST_FN' order by line;
TEXT
----------------------------------------------------------------------
function test_fn(test_date out varchar2)
RETURN varchar2
IS
BEGIN
select to_char(sysdate,'DD-MON-YY') into test_date from dual;
return test_date;
END test_fn;
7 rows selected.
test@ORA11G>
test@ORA11G> -- invoke this function from a SELECT statement
test@ORA11G> var x varchar2(20)
test@ORA11G>
test@ORA11G> select test_fn(:x) dt from dual;
select test_fn(:x) dt from dual
       *
ERROR at line 1:
ORA-06572: Function TEST_FN has out arguments

test@ORA11G>
test@ORA11G>

CREATE OR REPLACE FUNCTION test_fn
RETURN VARCHAR2
IS
BEGIN
  RETURN TO_CHAR(SYSDATE,'dd-mon-yy');
END test_fn;
/

test@ORA11G>
test@ORA11G> --
test@ORA11G> CREATE OR REPLACE FUNCTION test_fn
  2  RETURN VARCHAR2
  3  IS
  4  BEGIN
  5    RETURN TO_CHAR(SYSDATE,'dd-mon-yy');
  6  END test_fn;
  7  /
Function created.
test@ORA11G>
test@ORA11G> show errors
No errors.
test@ORA11G>
test@ORA11G>
test@ORA11G>
test@ORA11G> column x format a30
test@ORA11G> -- call the function from a SELECT statement
test@ORA11G>
test@ORA11G> select test_fn x from dual;
X
------------------------------
14-may-10
1 row selected.
test@ORA11G>
test@ORA11G> -- and now call the function in an anonymous PL/SQL block
test@ORA11G>
test@ORA11G> declare
  2    x  varchar2(20);
  3  begin
  4    x := test_fn;
  5    dbms_output.put_line('Value of x = '||x);
  6  end;
  7  /
Value of x = 14-may-10
PL/SQL procedure successfully completed.
test@ORA11G>
test@ORA11G>