If this is an SQL*Plus script you would simply need to use a HOST command. For example, change my script to:
Code:
spool myscript.sql

select 'HOST COPY x:\mydir\ORA' || ltrim(to_char(p.spid,'09999')) || '.TRC x:\mybackupdir\ctrl_to_trace.txt'
from v$process p, v$session s
where p.addr = s.paddr
and s.sid = (select sid from v$mystat where rownum=1);

spool off

@myscript.sql
On the other hand, if you are running this from a PL/SQL procedure, you should either use EXTPROC facility (you are limited to this option if you are using 8.0) or use some Java procedure from inside the database to copy files. If by any chance you are still using Oracle7 then your only option would be to use DBMS_PIPE. I'm sure you can find many scripts on the net that have samples of any and all of the above options.