#!/usr/bin/perl -w 

use strict;

print " please enter the domain name: ";

my  $targetdomain = <STDIN>;

chomp $targetdomain;

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

rename $file, "$file.bak" or die "Can't rename file '$file': $!\n";

open my $in, '<', "$file.bak" or die "Can't read file '$file': $!\n";
open my $out, '>', $file or die "Can't write file '$file': $!\n";

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

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

##</code><code>##

zone "foo"
{
    type "master";
    ...
};