Validate flags before login

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -10,12 +11,21 @@ import (
 	"github.com/GGP1/kure/commands/root"
 	"github.com/GGP1/kure/config"
 	"github.com/GGP1/kure/sig"
+	"github.com/spf13/pflag"
 
 	"github.com/awnumar/memguard"
 	bolt "go.etcd.io/bbolt"
 )
 
 func main() {
+	if err := validateFlags(); err != nil {
+		if errors.Is(err, pflag.ErrHelp) {
+			os.Exit(0)
+		}
+		fmt.Fprintln(os.Stderr, "error:", err)
+		os.Exit(1)
+	}
+
 	if err := config.Init(); err != nil {
 		fmt.Fprintln(os.Stderr, "couldn't initialize the configuration:", err)
 		os.Exit(1)
@@ -55,3 +65,24 @@ func main() {
 	db.Close()
 	memguard.SafeExit(0)
 }
+
+// validateFlags looks for the command called and parses its flags. If the flag is `--help`,
+// it will print the command's help message and return the error pflag.ErrHelp.
+func validateFlags() error {
+	cmd, args, err := root.NewCmd(nil).Find(os.Args[1:])
+	if err != nil {
+		return err
+	}
+
+	if err := cmd.ParseFlags(args); err != nil {
+		if errors.Is(err, pflag.ErrHelp) {
+			if err := cmd.Help(); err != nil {
+				return err
+			}
+			return pflag.ErrHelp
+		}
+		return err
+	}
+
+	return nil
+}