improve some error messages.

pkg/kubectl/cmd/exec.go

@@ -48,6 +48,10 @@ var (
 		kubectl exec 123456-7890 -c ruby-container -i -t -- bash -il`)
 )
 
+const (
+	execUsageStr = "expected 'exec <pod-name> <command> [arg1] [arg2] ... [argN]'.\n<pod-name> and <command> are required parameter for the exec command"
+)
+
 func NewCmdExec(f *cmdutil.Factory, cmdIn io.Reader, cmdOut, cmdErr io.Writer) *cobra.Command {
 	options := &ExecOptions{
 		StreamOptions: StreamOptions{
@@ -135,19 +139,19 @@ type ExecOptions struct {
 func (p *ExecOptions) Complete(f *cmdutil.Factory, cmd *cobra.Command, argsIn []string, argsLenAtDash int) error {
 	// Let kubectl exec follow rules for `--`, see #13004 issue
 	if len(p.PodName) == 0 && (len(argsIn) == 0 || argsLenAtDash == 0) {
-		return cmdutil.UsageError(cmd, "POD is required for exec")
+		return cmdutil.UsageError(cmd, execUsageStr)
 	}
 	if len(p.PodName) != 0 {
-		printDeprecationWarning("exec POD", "-p POD")
+		printDeprecationWarning("exec <pod-name>", "-p <pod-name>")
 		if len(argsIn) < 1 {
-			return cmdutil.UsageError(cmd, "COMMAND is required for exec")
+			return cmdutil.UsageError(cmd, execUsageStr)
 		}
 		p.Command = argsIn
 	} else {
 		p.PodName = argsIn[0]
 		p.Command = argsIn[1:]
 		if len(p.Command) < 1 {
-			return cmdutil.UsageError(cmd, "COMMAND is required for exec")
+			return cmdutil.UsageError(cmd, execUsageStr)
 		}
 	}
 

pkg/kubectl/cmd/logs.go

@@ -53,6 +53,10 @@ var (
 		kubectl logs --since=1h nginx`)
 )
 
+const (
+	logsUsageStr = "expected 'exec <pod-name> [container-name]'.\n<pod-name> is a required parameter for the logs command"
+)
+
 type LogsOptions struct {
 	Namespace   string
 	ResourceArg string
@@ -111,17 +115,17 @@ func (o *LogsOptions) Complete(f *cmdutil.Factory, out io.Writer, cmd *cobra.Com
 	containerName := cmdutil.GetFlagString(cmd, "container")
 	switch len(args) {
 	case 0:
-		return cmdutil.UsageError(cmd, "POD is required for logs")
+		return cmdutil.UsageError(cmd, logsUsageStr)
 	case 1:
 		o.ResourceArg = args[0]
 	case 2:
 		if cmd.Flag("container").Changed {
-			return cmdutil.UsageError(cmd, "only one of -c, [CONTAINER] arg is allowed")
+			return cmdutil.UsageError(cmd, "only one of -c or an inline [CONTAINER] arg is allowed")
 		}
 		o.ResourceArg = args[0]
 		containerName = args[1]
 	default:
-		return cmdutil.UsageError(cmd, "logs POD [-c CONTAINER]")
+		return cmdutil.UsageError(cmd, logsUsageStr)
 	}
 	var err error
 	o.Namespace, _, err = f.DefaultNamespace()

pkg/kubectl/cmd/scale.go

@@ -101,11 +101,6 @@ func RunScale(f *cmdutil.Factory, out io.Writer, cmd *cobra.Command, args []stri
 		printDeprecationWarning("scale", "resize")
 	}
 
-	count := cmdutil.GetFlagInt(cmd, "replicas")
-	if count < 0 {
-		return cmdutil.UsageError(cmd, "--replicas=COUNT is required, and COUNT must be greater than or equal to 0")
-	}
-
 	cmdNamespace, enforceNamespace, err := f.DefaultNamespace()
 	if err != nil {
 		return err
@@ -120,10 +115,18 @@ func RunScale(f *cmdutil.Factory, out io.Writer, cmd *cobra.Command, args []stri
 		Flatten().
 		Do()
 	err = r.Err()
+	if resource.IsUsageError(err) {
+		return cmdutil.UsageError(cmd, err.Error())
+	}
 	if err != nil {
 		return err
 	}
 
+	count := cmdutil.GetFlagInt(cmd, "replicas")
+	if count < 0 {
+		return cmdutil.UsageError(cmd, "The --replicas=<count> flag is required, and <count> must be greater than or equal to 0")
+	}
+
 	infos := []*resource.Info{}
 	err = r.Visit(func(info *resource.Info, err error) error {
 		if err == nil {

pkg/kubectl/resource/builder.go

@@ -78,6 +78,21 @@ type Builder struct {
 	schema validation.Schema
 }
 
+var missingResourceError = fmt.Errorf(`You must provide one or more resources by argument or filename.
+Example resource specifications include:
+   '-f rsrc.yaml'
+   '--filename=rsrc.json'
+   'pods my-pod'
+   'services'`)
+
+// TODO: expand this to include other errors.
+func IsUsageError(err error) bool {
+	if err == nil {
+		return false
+	}
+	return err == missingResourceError
+}
+
 type resourceTuple struct {
 	Resource string
 	Name     string
@@ -700,7 +715,7 @@ func (b *Builder) visitorResult() *Result {
 	if len(b.resources) != 0 {
 		return &Result{err: fmt.Errorf("resource(s) were provided, but no name, label selector, or --all flag specified")}
 	}
-	return &Result{err: fmt.Errorf("you must provide one or more resources by argument or filename (%s)", strings.Join(InputExtensions, "|"))}
+	return &Result{err: missingResourceError}
 }
 
 // Do returns a Result object with a Visitor for the resources identified by the Builder.