converter pgplsql funcion

I work with oracle and have poor experience in pg/plsql.
anybody can  help me  with translate from   pl/sql in pg/plsql in code below:

CREATE OR REPLACE FUNCTION clean_string(p_dado varchar2) RETURN varchar2
IS
  v_clean_string varchar(4000);
BEGIN
    v_clean_string := p_dado;
     for r in (select caracter from caracteres) loop
          select replace(v_clean_string,r.caracter,'')
         into v_clean_string
         from dual;
    end loop;
    return v_clean_string;
END;
/

need funcion in pg/plsql
thanks for help