create-tracker = {
	trackingContext = $1
	trackedClass = $2
	serviceAdded = $3
	serviceRemoved = $4
	shellClassLoader = (($.session class) getClassLoader)
	arrayClass = ($shellClassLoader loadClass java.lang.reflect.Array)
	handler = {
		proxy = $1
		method = $2
		arguments = $3
		name = ($method name)
		# echo "Invoking $name"
		if { $name equals "addingService" } \
		then {
			ref = ($arrayClass get $arguments 0)
			svc = ($.context getService $ref)
			$serviceAdded execute $.commandSession [ $svc ]
			$svc
		} elif { $name equals "removedService" } \
		then {
			ref = ($arrayClass get $arguments 0)
			svc = ($arrayClass get $arguments 1)
			$serviceRemoved execute $.commandSession [ $svc ]
			$.context ungetService $ref
		}
	}
	# create handler
	customizerClass = ($shellClassLoader loadClass org.osgi.util.tracker.ServiceTrackerCustomizer)
	array = ([ $customizerClass ] toArray ($arrayClass newInstance "java.lang.Class" 1))
	proxyClass = ($shellClassLoader loadClass java.lang.reflect.Proxy)
	customizer = ($proxyClass newProxyInstance $shellClassLoader $array $handler)
	# create tracker
	trackerClass = ($shellClassLoader loadClass org.osgi.util.tracker.ServiceTracker)
	constructor = ($trackerClass constructor org.osgi.framework.BundleContext java.lang.String org.osgi.util.tracker.ServiceTrackerCustomizer)
	if { "java.lang.Class" equals ($trackedClass class) } \
	then {
		trackedClass = ($trackedClass name)
	}
	tracker = ($constructor newInstance $trackingContext $trackedClass $customizer)
	$tracker
}

tracker = (create-tracker $.context "org.osgi.service.cm.ManagedService" { s = (($1 class) toString); echo "service-added $s" } { s = (($1 class) toString); echo "service-removed $s" })
$tracker open true