diff --git a/main.go b/main.go
index 32a7316..59472ce 100644
--- a/main.go
+++ b/main.go
@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
+	"os"
+	"os/exec"
 	"path"
 	"strconv"
 	"strings"
@@ -113,7 +115,7 @@ func getTime(timeString string) (int, int) {
 	return int(hr), int(min)
 }
 
-func getNextWait(config sunsetConfig) string {
+func getNextWait(config sunsetConfig) (int, int) {
 	index := nextIndex(config)
 	now := time.Now()
 	nextHr, nextMin := getTime(config.Files[index].Time)
@@ -123,7 +125,6 @@ func getNextWait(config sunsetConfig) string {
 
 	// FIXME still not working
 	if now.Hour() >= nextHr && now.Minute() >= nextMin {
-		fmt.Print("u")
 		diffHr = 24 - (now.Hour() - nextHr)
 		diffMin = 60 - (now.Minute() - nextMin)
 	} else {
@@ -131,12 +132,31 @@ func getNextWait(config sunsetConfig) string {
 		diffMin = nextMin - now.Minute()
 	}
 
-	return fmt.Sprintf("%dh%dm", diffHr, diffMin)
+	return diffHr, diffMin
+}
+
+func block(config sunsetConfig, command string) {
+	for {
+		nextHr, nextMin := getNextWait(config)
+		timer := time.NewTimer((time.Duration(nextHr) * time.Hour) + (time.Duration(nextMin) * time.Minute))
+		<-timer.C
+		go runCommand(command)
+	}
+}
+
+func runCommand(command string) {
+	cmd := exec.Command("/usr/bin/env sh", "-c", command)
+	err := cmd.Run()
+	if err != nil {
+		log.Printf("Command %s returned a non 0 code", command)
+	}
 }
 
 func main() {
 	printNextTime := flag.Bool("next", false, "Print the time to the next change")
 	printNextWait := flag.Bool("wait", false, "Print the time to wait for the next change")
+	blockFlag := flag.Bool("block", false, "Block and call the provided command when the background changes")
+	blockCommand := flag.String("command", "", "Specify a command to run when the background changed")
 	configFile := flag.String("file", "./sunset.json", "Specify the file to load")
 	flag.Parse()
 
@@ -145,7 +165,15 @@ func main() {
 	if *printNextTime {
 		fmt.Printf("%s", getNextTime(conf))
 	} else if *printNextWait {
-		fmt.Printf("%s", getNextWait(conf))
+		hr, min := getNextWait(conf)
+		fmt.Printf("%dh%dm", hr, min)
+
+	} else if *blockFlag {
+		if *blockCommand == "" {
+			fmt.Println("Must provide a command.")
+			os.Exit(1)
+		}
+		block(conf, *blockCommand)
 	} else {
 		index := currentIndex(conf)
 		absoluteImagePath := path.Join(path.Dir(*configFile), conf.Files[index].File)