sub line_num {
   my $total_lines = shift;
   my $line_number = ($t->index('insert'));
   print $line_number,"\n";

   $linenumbers->delete("1.0", "end");
   for (0..$total_lines) {
      $linenumbers->insert('end', join "\n", map {sprintf "%4d", $_ } $_);
   }
   #$linenumbers->yviewMoveto($line_number/$total_lines);
   #$linenumbers->yview(-pickplace, $line_number);
   $linenumbers->see($line_number);
}