Add flag to only generate registry overview once (#29)

Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>

server/server.go

@@ -70,6 +70,10 @@ func main() {
 			Name:  "insecure, k",
 			Usage: "do not verify tls certificates of registry",
 		},
+		cli.BoolFlag{
+			Name:  "once, o",
+			Usage: "generate an output once and then exit",
+		},
 		cli.StringFlag{
 			Name:  "port",
 			Value: "8080",
@@ -183,6 +187,11 @@ func main() {
 			logrus.Fatalf("Error creating index: %v", err)
 		}
 
+		if c.GlobalBool("once") {
+			logrus.Info("Output generated")
+			return nil
+		}
+
 		// parse the duration
 		dur, err := time.ParseDuration(c.String("interval"))
 		if err != nil {