Add simple verification command to test if the backup is readable

cmd/check.go

@@ -0,0 +1,43 @@
+package cmd
+
+import (
+	"io/ioutil"
+	"log"
+	"os"
+
+	"github.com/pkg/errors"
+	"github.com/urfave/cli"
+)
+
+// Check fulfils the `format` subcommand.
+var Check = cli.Command{
+	Name:               "check",
+	Usage:              "Verify that a backup is readable",
+	UsageText:          "Attempts to decrypt the provided backup and do nothing with it except verify that it's readable\n from start to finish. Enables verbose logging by default.",
+	CustomHelpTemplate: SubcommandHelp,
+	Flags: []cli.Flag{
+		cli.StringFlag{
+			Name:  "password, p",
+			Usage: "use `PASS` as password for backup file",
+		},
+		cli.StringFlag{
+			Name:  "pwdfile, P",
+			Usage: "read password from `FILE`",
+		},
+	},
+	Action: func(c *cli.Context) error {
+		bf, err := setup(c)
+		if err != nil {
+			return err
+		}
+
+		log.SetOutput(os.Stderr)
+
+		if err := Raw(bf, ioutil.Discard); err != nil {
+			return errors.Wrap(err, "Encountered error while checking")
+		}
+
+		log.Println("Backup looks okay from here.")
+		return nil
+	},
+}

main.go

@@ -23,6 +23,7 @@ func main() {
 		cmd.Format,
 		cmd.Analyse,
 		cmd.Extract,
+		cmd.Check,
 	}
 	app.Flags = []cli.Flag{
 		cli.BoolFlag{