use strict;
use warnings;
use 5.0080;

my $html =<<'HTML';
<div>
	<p>Code</p>
	<?perl 
		my $string = "Hello World";
		"<b>$string</b>";	
	?>
</div>
HTML

$html =~ s/\<\?perl(.*?)\?\>/(sub{$1})->()/gisee;

print $html;