you method is depend on creating backup

No, it doesn't depend on that, it just does it. Changing that bit is trivial:

#!/usr/bin/perl -w 

use strict;

print " please enter the domain name: ";

my  $targetdomain = <STDIN>;

chomp $targetdomain;

my  $file = "/home/blackice/hello";

open my $fh, '<', $file or die "Can't read '$file': $!\n";
my @array = <$fh>;
close $fh or die "Can't close file '$file' properly: $!\n";

my $comment = 0;
my $block   = 0;

for (@array) {
    if (/^zone\s+"$targetdomain"/) {
        $comment++;
        $block += () = /(\{)/g;
        print $out '// '.$_; next;
    }
    if($comment) {
        $block += () = /(\{)/g;
        s!^!// ! if $comment or $block;
        $block -= () = /(\})/g;
        $comment = 0 unless $block;
    }
}

open $fh, '>', $file or die "Can't write '$file': $!\n";
print $fh @array;
close $fh or die "Can't close file '$file' properly: $!\n";
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