SQL> with data as (
  2    select '112233' val from dual
  3    union all
  4    select '1223568' from dual
  5    union all
  6    select '112233 hey man...' from dual
  7    union all
  8    select '112233xxxyyy' from dual
  9    )
 10  select val from data
 11  where regexp_like(val,'^[[:digit:]]{6}($| .)')
 12  /
VAL
-----------------
112233
112233 hey man...

2 rows selected.

declare 
  rt_vc_arr owa_text.vc_arr;
  s_message varchar(20) := '123456asdf';
begin
  IF owa_pattern.match(line =>s_message,                         
                        pat => ???
                        backrefs => rt_vc_arr,
                        flags   => 'i')
    THEN ......
  ELSE
    ....
  END IF;                             
end;

SQL> declare 
  2    rt_vc_arr owa_text.vc_arr;
  3    s_message varchar(20) := '123456asdf';
  4  begin
  5    IF regexp_like(s_message,'^[[:digit:]]{6}($| .)')
  6      THEN null;
  7    ELSE
  8      null;
  9    END IF;                             
 10  end;
 11  /

PL/SQL procedure successfully completed.

SQL> declare 
  2    rt_vc_arr owa_text.vc_arr;
  3    s_message varchar(20) := '123456asdf';
  4    now integer;
  5  begin
  6    now := dbms_utility.get_time();
  7    for i in 1..100000 loop
  8      s_message := dbms_random.string ('a', 10);
  9      IF owa_pattern.match(line =>s_message,                         
 10                            pat => '^\d{6}[\s\$]',
 11                            backrefs => rt_vc_arr,
 12                            flags   => 'i')
 13        THEN null;
 14      ELSE
 15        null;
 16      END IF;                             
 17    end loop;
 18    dbms_output.put_line('owa_pattern: '||((dbms_utility.get_time()-now)/100)||'s');
 19    now := dbms_utility.get_time();
 20    for i in 1..100000 loop
 21      s_message := dbms_random.string ('a', 10);
 22      IF regexp_like(s_message,'^[[:digit:]]{6}($| .)')
 23        THEN null;
 24      ELSE
 25        null;
 26      END IF;                             
 27    end loop;
 28    dbms_output.put_line('regexp_like: '||((dbms_utility.get_time()-now)/100)||'s');
 29  end;
 30  /
owa_pattern: 27.11s
regexp_like: 2.51s

PL/SQL procedure successfully completed.

declare 
  rt_vc_arr owa_text.vc_arr;
  s_mess_body varchar(20) := 'ABCDEF 160 685';
begin
  IF owa_pattern.match (line   => s_mess_body, 
                        pat      => '^[A-Za-z#]+\s(\d+)\s(\d+)[\s\$]',
                        backrefs => rt_vc_arr,
                        flags    => 'i')
    THEN dbms_output.put_line('rt_vc_arr(1) '||rt_vc_arr(1));
         dbms_output.put_line('rt_vc_arr(2) '||rt_vc_arr(2));         
  ELSE
    dbms_output.put_line('nothing found!!!'); 
  END IF;                             
end;