You can change your loop code to be as follows:

for($i = 0; $i < @contents; $i++){
      if($contents{$i] =~ m/manager\.(\d*)\.address=(\d*\.\d*\.\d*\.\d
+*)/) {
       if($address eq "$2"){
            print "manager.$1.address=$2\n";
            print " exist at index $i\n";
        }
   }
}
[download]

-albert

Update: editing the suggestion for the lack of $_ in the solution. Untested code, your mileage may vary.