Bind variables can be of type IN, OUT, or IN OUT.
By default, all parameters are of type IN.
Using an OUT Parameter
SQL> declare
2 a NUMBER;
3 b NUMBER:=1;
4 c NUMBER:=2;
5 v_plsql_tx VARCHAR2(2000);
6 begin
7 v_plsql_tx := 'begin ' || ':1:=:2 -:3; ' || 'end;';
8 execute immediate v_plsql_tx using out a, b, c;
9 DBMS_OUTPUT.put_line('a='||a);
10 end;
11 /
a=-1
PL/SQL procedure successfully completed.
SQL>