How to get the directory path from a full path

CREATE OR REPLACE FUNCTION get_dir_path (p_file IN VARCHAR2) RETURN varchar2
IS
v_dir_path VARCHAR2(1000);
BEGIN
/*
|| This Function returns a varchar2 string of the directory path of the file name. — not including trailing slash.
|| Written by: Daniel Coe
|| Date: 10/09/2002
*/
BEGIN

IF instr(p_file,’/’) > 0 THEN — Unix

v_dir_path := substr(p_file,1,(instr(p_file,’/’,-1,1)-1));

ELSIF instr(p_file,’\’) > 0 THEN — Windows

v_dir_path := substr(p_file,1,(instr(p_file,’\’,-1,1)-1));

END IF;

EXCEPTION
WHEN value_error THEN
v_dir_path := sqlerrm;

END;

RETURN v_dir_path;
END;
/