Better Usage func

main.go

@@ -2,7 +2,9 @@ package main
 
 import (
 	"flag"
+	"fmt"
 	"log"
+	"os"
 	"runtime"
 )
 
@@ -10,17 +12,35 @@ import (
 // builds and returns
 type command func() error
 
+var usage = fmt.Sprintf(
+	`Usage: vegeta [globals] <command> [options]
+
+Commands:
+  attack  Hit the targets
+  report  Report the results
+
+Globals:
+  -cpus=%d Number of CPUs to use
+`, runtime.NumCPU())
+
+func init() {
+	flag.Usage = func() { fmt.Print(usage) }
+	cpus := flag.Int("cpus", runtime.NumCPU(), "Number of CPUs to use")
+	flag.Parse()
+	runtime.GOMAXPROCS(*cpus)
+}
+
 func main() {
 	commands := map[string]func([]string) command{
 		"attack": attackCmd,
 		"report": reportCmd,
 	}
-	// Global flags
-	cpus := flag.Int("cpus", runtime.NumCPU(), "Number of CPUs to use")
-	flag.Parse()
-	args := flag.Args()
 
-	runtime.GOMAXPROCS(*cpus)
+	args := flag.Args()
+	if len(args) == 0 {
+		flag.Usage()
+		os.Exit(1)
+	}
 
 	if cmd, ok := commands[args[0]]; !ok {
 		log.Fatalf("Unknown command: %s", args[0])