DB<1> $t=time;for (1..10000000) {$str="";$str.="a"."b";};print time-$t
10
  DB<2> $t=time;for (1..10000000) {$str="";$str=$str."a";$str.="b";};print time-$t
17
  DB<3> $t=time;for (1..10000000) {$str="";$str=$str."a"."b";};print time-$t
15