In the GuiXT script you can use:

Enter  process="myscript.txt"

Please make sure you have an appropriate if...endif around the Enter statement, otherwise an infinite loop is started if the InputScript stays on this screen. You can use:

// first time during this transaction?

if not V[_transactionid=&V[prev_transactionid]]

  Set V[prev_transactionid] "&V[_transactionid]"

  Enter process="myscript.txt"

endif

or a similar mechanism, using a V-variable that you set in the InputScript.

If an infinite loop does occur during testing (flickering screen), press the "Visible" button in GuiXT window and change the script.