SQL & PL/SQL

Hi all ,
Please help me in this dbt .
in one article i saw

UTL_FILE_DIR lets you specify one or more directories that Oracle should use for PL/SQL file I/O. If you are specifying multiple directories, you must repeat the UTL_FILE_DIR parameter for each directory
on separate lines of the initialization parameter file

and in another alter system set utl_file_dir=dir1,dir2 scope=both;

whther the second method is possible

if i want to have a directory and its sub directory to set in utl_file_dir
what i should do , whether i want to specify main directory and all sub directory seperated by comma or any other method is there

Please help me

thanks in advance ..........