How to pass value by using SQL*PLUS

Question

Dear all,
I have a file (e.g. test.sql) and run in SQL*PLUS. The code like the following:
set serveroutput on
variable v_a number;
variable v_b number;
variable v_x number;
:v_x := 12345;
execute packagename.procedure(:v_x, :v_a, :v_b);
print v_a;
print v_b;
Why it does not work??
Thanks for any advice.
Regrads.

Answer 1

Test it:
set ver off;
set serveroutput on
variable v_a number;
variable v_b number;
variable v_x number;
accept v_a prompt 'Input value for v_a: '
accept v_b prompt 'Input value for v_b: '
accept v_x prompt 'Input value for v_x: '
begin
  :v_a := &v_a;
  :v_b := &v_b;
  :v_x := &v_x;
end;
print v_a;
print v_b;
print v_x;