rhqadmin@pintsize:7080$ exporter.file = 'somewhere/over/the/rainbow'
rhqadmin@pintsize:7080$ exporter.format = 'csv'
rhqadmin@pintsize:7080$ var start = new Date() - 8* 3600 * 1000;                                   
rhqadmin@pintsize:7080$ var end = new Date()
rhqadmin@pintsize:7080$ var data = MeasurementDataManager.findDataForResource(10003,[10473],start,end,60)
rhqadmin@pintsize:7080$ exporter.write(data.get(0))

where 10003 is the resource id and 10473 is the metric definition id. You can get this e.g. from the big chart's url:

http://pintsize:7080/resource/common/monitor/Visibility.do?mode=chartSingleMetricSingleResource&id=10003&m=10473

The "data.get(0)" bit is important because the findDataForResource method returns a list of lists, where each "inner" list corresponds to the index of the metric id in the provided array of metric ids ([10473])). And thus the data.get(0) contains the data for the first metric (and only) metric you asked for. The exporter cannot handle the "list of lists" in csv format.