Don't run with --help or an unknown flag

Co-authored-by: Danail Branekov <danailster@gmail.com>

integration/integration_test.go

@@ -338,6 +338,30 @@ var _ = Describe("Integration", func() {
 			Eventually(gdnSession).Should(gexec.Exit(131))
 		})
 	})
+
+	When("passed the --help flag", func() {
+		BeforeEach(func() {
+			cmd.Args = append(cmd.Args, "--help")
+		})
+
+		It("prints the usage and exits", func() {
+			Expect(session.ExitCode()).To(Equal(0))
+			Expect(session).To(gbytes.Say("Usage"))
+			Expect(filepath.Join(sandboxDir, "var/vcap/data/tmp/")).NotTo(BeADirectory())
+		})
+	})
+
+	When("passed an unknown flag", func() {
+		BeforeEach(func() {
+			cmd.Args = append(cmd.Args, "--hello")
+		})
+
+		It("prints the usage and exits", func() {
+			Expect(session.ExitCode()).To(Equal(1))
+			Expect(session.Err).To(gbytes.Say("unknown flag"))
+			Expect(filepath.Join(sandboxDir, "var/vcap/data/tmp/")).NotTo(BeADirectory())
+		})
+	})
 })
 
 func tarballShouldContainFile(tarballPath, filePath string) {

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -32,7 +33,7 @@ func main() {
 		SigQUIT bool `long:"sigquit" description:"Send a SIGQUIT to the gdn process"`
 	}
 
-	flags.ParseArgs(&opts, os.Args)
+	handleFlagErrors(flags.ParseArgs(&opts, os.Args))
 
 	checkIsRoot()
 	checkIsNotBpm()
@@ -154,3 +155,14 @@ func createReportDir(baseDir string) string {
 	}
 	return path
 }
+
+func handleFlagErrors(_ []string, err error) {
+	flagErr := &flags.Error{}
+	if errors.As(err, &flagErr) && flagErr.Type == flags.ErrHelp {
+		os.Exit(0)
+	}
+
+	if err != nil {
+		os.Exit(1)
+	}
+}