* the entire output as the body of a event. It takes two arguments - the
* command to run, and a time period to sleep in millis before executing
* again.
*/
public static SourceBuilder buildPeriodic() {
return new SourceBuilder() {
@Override
public EventSource build(String... argv) {
Preconditions.checkArgument(argv.length == 2,
"execPeriodic(\"cmdline \",period)");
String command = argv[0];