my $string = '<div > <div > </div><div > not_show_1 </div> </div> show_1 <div > <div > <div > not_show_2 </div> </div> </div> show_2';
$string =~ s!<div[^>]+>[^<]+</div>!!g while($string =~ m/<div[^>]+>/);
print $string . "\n";