Report incorrect or missing commands

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"flag"
+	"fmt"
 	"os"
 	"bufio"
 	"io"
@@ -12,6 +13,11 @@ import (
 func main() {
 	flag.Parse()
 
+	if len(flag.Args()) < 2 {
+		fmt.Println("Too few args specified. Supported commands are 'times', 'unique' and 'hang'.")
+		os.Exit(1)
+	}
+
 	var p core.Progress
 	switch flag.Arg(0) {
 	case "times":
@@ -20,10 +26,14 @@ func main() {
 		p = core.NewProgressUniques()
 	case "hang":
 		p = core.NewProgressHangs()
+	default:
+		fmt.Printf("Invalid command: '%s'. Supported commands are 'times', 'unique' and 'hang'.\n", flag.Arg(0))
+		os.Exit(1)
 	}
 
 	var line string
 	for i := 1; i < flag.NArg(); i++ {
+		fmt.Printf("--------  %s  --------\n", flag.Arg(i))
 		progressFile, err := os.Open(flag.Arg(i))
 		if err != nil {
 			panic(err)