Select Code to Download

$string =~ s/(\Q$first\E).*?(\Q$last\E)/$1$reserve$2/;

$string =~ s/(?<=\Q$first\E).*?(?=\Q$last\E)/$reserve/;

$first_start = index($_, $first);
if ($first_start >= 0) {
...
      substr($_, $first_end, $last_start, $replace);
   }
}