my $str = <<'END';
Hello
# START
World
# END
Aaa
# START
Bbb
# END
Ccc
END

open my $fh, '<', \$str or die $!;
while (<$fh>) {
	chomp;
	if ( /^# START/ .. /^# END/ ) {
		print "<$_>\n";
	}
}
close $fh;