Try the following from Arpan's script:

// Batch Update records
while (true) {
	var needit_gr = new GlideRecord('insert_the_name_of_the_needit_table');
	needit_gr.addNullQuery('u_requested_for_email');
	needit_gr.setLimit(100);
	needit_gr.query();
	var numberRecs = needit_gr.getRowCount();
	// see if we're done, if so exit while loop
	if (numberRecs == 0)
		break;
	gs.info("Batch update records: found " + numberRecs + " to process.");
	while(needit_gr.next()){
		needit_gr.setValue('u_requested_for_email', needit_gr.u_requested_for.email);
		needit_gr.update();
	}
}