retentioncell := 1;

declare

cur PLS_INTEGER := DBMS_SQL.OPEN_CURSOR;
fdbk PLS_INTEGER;

local_var varchar2(100);
var_1 varchar2(100) := 'retentioncell';
retentioncell number;

begin

retentioncell := 1;

DBMS_SQL.PARSE (cur, 'BEGIN :tmp := :tmp2; END;' ,2);
DBMS_SQL.BIND_VARIABLE (cur, 'tmp', '                 ');
DBMS_SQL.BIND_VARIABLE (cur, 'tmp2', var_1);
fdbk := DBMS_SQL.EXECUTE (cur);
DBMS_SQL.VARIABLE_VALUE (cur, 'tmp', local_var);

dbms_output.put_line(local_var);

end;

SQL> create or replace package pkg_t
  2  is
  3    public_var number := 10;
  4  end;
  5  /
 
Package created.
 
SQL> declare
  2   varname varchar2(30) := 'public_var';
  3   value number;
  4  begin
  5   execute immediate 'begin :1 := pkg_t.' || varname || '; end;' using out value;
  6   dbms_output.put_line(value);
  7  end;
  8  /
10
 
PL/SQL procedure successfully completed.