SQL> create or replace procedure p_test (par_deptno in emp.deptno%type,
  2                                      par_msg   out varchar2)
  3  is
  4    l_ename emp.ename%type;
  5  begin
  6    select e.ename
  7      into l_ename
  8      from emp e
  9      where e.deptno = par_deptno;
 10  exception
 11    when too_many_rows then
 12      par_msg := 'There are too many rows returned by the query';
 13    when others then
 14      par_msg := 'Unknown error; code = ' || sqlcode;
 15  end;
 16  /

Procedure created.

SQL> declare
  2    l_out varchar2(200);
  3  begin
  4    p_test (&v_deptno, l_out);
  5    dbms_output.put_line(l_out);
  6  end;
  7  /
Enter value for v_deptno: 10
There are too many rows returned by the query

PL/SQL procedure successfully completed.

SQL> /
Enter value for v_deptno: 99
Unknown error; code = 100

PL/SQL procedure successfully completed.

SQL>