oracle substr stored proc

create or replace
PROCEDURE TESTHM AS
BEGIN
    dbms_output.put_line ('TestHm');
    DECLARE str VARCHAR2(4000);
    BEGIN
        FOR r IN (SELECT * FROM myTable where rownum<=5)
        LOOP
            str:=SUBSTR(r.myStrField,1, 10);     
            dbms_output.put_line( str );
            dbms_output.put_line( r.myStrField);
        END LOOP;
    END;   

    dbms_output.put_line (CURRENT_DATE);
END TESTHM;