a bunch of updates, including verify function

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

cmd/image.go

@@ -3,6 +3,9 @@ package cmd
 import (
 	"context"
 	"fmt"
+	"os"
+
+	"github.com/pkg/errors"
 
 	"github.com/hairyhenderson/go-onerng"
 	"github.com/spf13/cobra"
@@ -10,17 +13,34 @@ import (
 
 // imageCmd represents the image command
 func imageCmd(ctx context.Context) *cobra.Command {
-	return &cobra.Command{
+	var imgOut string
+	cmd := &cobra.Command{
 		Use:   "image",
 		Short: "Dump the OneRNG's firmware image",
 		RunE: func(cmd *cobra.Command, args []string) error {
 			o := onerng.OneRNG{Path: opts.Device}
+			err := o.Init(ctx)
+			if err != nil {
+				return errors.Wrapf(err, "init failed before image extraction")
+			}
 			image, err := o.Image(ctx)
 			if err != nil {
 				return err
 			}
-			fmt.Printf("%q\n", image)
-			return nil
+			var out *os.File
+			if imgOut == "-" {
+				out = os.Stdout
+			} else {
+				out, err = os.OpenFile(imgOut, os.O_RDWR|os.O_CREATE, 0644)
+				if err != nil {
+					return err
+				}
+			}
+			n, err := out.Write(image)
+			fmt.Fprintf(os.Stderr, "Wrote %db to %s\n", n, imgOut)
+			return err
 		},
 	}
+	cmd.Flags().StringVarP(&imgOut, "out", "o", "onerng.img", "output file for image (use - for stdout)")
+	return cmd
 }