Requires support for long-running tasks, ie progress bar. Indeterminate bar, plus progress bar when the script is able to say what % complete it is.
Until this is implemented the only to get feedback is to write to the logs, eg every 20 issues you process, write a log message:
log.warn ("Processed $n of $m issues")
log.warn ("Completed, $m issues")
You can use the built-in script "View Server Logs" to "tail" the log file while your script runs.