Created One Trigger in Oracle..

SQL> CREATE OR REPLACE TRIGGER student_after_insert
  2  AFTER INSERT
  3  ON student
  4  FOR EACH ROW
  5  BEGIN
  6     @hello.pl
  9  END student_after_insert;
 10  /

Contents of hello.pl are:-

BEGIN
   DBMS_OUTPUT.PUT_LINE('hello world');
END;

And.. the result is pretty good, as the content of hello.pl is displayed on screen while inserting a record..

Now, the query is -- When i change the content of the hello.pl file, after exiting from oracle, and then logging again, It doesn't shows the updated contents, instead it shows the previous content..

I noticed that, if i drop the trigger and create it again, then it is working fine.. Why is it happening so.. And what is the solution to this problem..