out parameter is supposed to read by another program like a front end.
you can create another procedure in sqlplus to read and display the out parameter
or
use a place holder like this

  1  create or replace procedure test1
  2  (name in varchar2,
  3   osal  out number)
  4  as
  5  begin
  6  select sal into osal from emp where ename =name;
  7* end;
dbadmin@mutation_mutation > /

Procedure created.

dbadmin@mutation_mutation > save test1
Created file test1.sql
dbadmin@mutation_mutation > variable a number;
dbadmin@mutation_mutation > exec test1('KING',:a);

PL/SQL procedure successfully completed.

dbadmin@mutation_mutation > print :a

         A
----------
      5000

dbadmin@mutation_mutation >