perl按固定长度分裂字符串

$a="111111111111111111111111111111111111";
@b = $a =~ /\w{3}/g;
print "@b\n";

@c = unpack("(A3)*", $a);
print "$c[7]\n";

for ($i=1;$i<=13;$i=$i+3)
{
$b=substr($a,$i,3);
push @d,$b;
}
print "@d";