:P ...guru, awake now :)

Thanks. That was super rapid!

I ran GoTk.pm. I do a small change in $mw->Entry, then I close the first $mw, I reran and I saw the text change in the secondly created window. (understood that I closed the first mainwindow to save changes to the $file !)

My need is, when I re-run, I should 'add' new tab to a notebook in first opened $mw itself. My need is not saving values from the first $mw on WM_DELETE_WINDOW event but updating the existing mainwindow.

any chance for this ?

if this is not possible, then is it possible to trigger a timer kind of thing from the GUI itself to check for updates on a file (at regular interval) and when the file is updated with a new line, the GUI adds a new tab.

...