Thankx everybody for ur interest.... on this I modified my code like following ...

use Win32::ChangeNotify;
print " \n Enter a file path ";
$pt = <STDIN>;
chomp $pt;
$notify = Win32::ChangeNotify->new($pt, true ,"SIZE");
$cnt = 0;

while(1)
{
$cnt++;
if ($cnt > 1) {
    print " \n File copy is going on ";
    $notify->reset;
}
 $lmt--;
 next if ($notify->wait(10000));
 print " \n The counter value is $cnt \n ";
 last;
  }

print " \n hello world ";
$notify->Close();
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after I set one file for copy if I execute the script it will only show the result as following: "The counter value is 1" "hello world ." That means it is not iterating through the loop after 1 st wait call because wait call unable to get signalled within 10000 milliseonds although hfe file copy still is going on.. . I think because while copying windows allocates size priorly in the destination as same size of source thats why although its being copied and getting increased in sized.. the $notify->wait(10000) call unable to detect the changes in filesize.