use strict;

open(my $In, '<', "C:/Windows/System32/drivers/etc/hosts") or die $!;
my @Output = <$In>;
map{if($_ =~ /^(#)?(10\.10\.1\.2.*)/){$_ = $1 eq '#' ? $2 : "#$2";}} @Output;
close $In;

open(Out, '>', "C:/Windows/System32/drivers/etc/hosts") or die $!;
print Out @Output;