Add --dry-run option for label command

contrib/completions/bash/kubectl

@@ -820,6 +820,7 @@ _kubectl_label()
     flags_completion=()
 
     flags+=("--all")
+    flags+=("--dry-run")
     flags+=("--filename=")
     flags_with_completion+=("--filename")
     flags_completion+=("__handle_filename_extension_flag json|yaml|yml")

docs/man/man1/kubectl-label.1

@@ -27,6 +27,10 @@ If \-\-resource\-version is specified, then updates will use this resource versi
     select all resources in the namespace of the specified resource types
 
 .PP
+\fB\-\-dry\-run\fP=false
+    If true, only print the object that would be sent, without sending it.
+
+.PP
 \fB\-f\fP, \fB\-\-filename\fP=[]
     Filename, directory, or URL to a file identifying the resource to update the labels
 

docs/user-guide/kubectl/kubectl_label.md

@@ -75,6 +75,7 @@ $ kubectl label pods foo bar-
 
 ```
       --all[=false]: select all resources in the namespace of the specified resource types
+      --dry-run[=false]: If true, only print the object that would be sent, without sending it.
   -f, --filename=[]: Filename, directory, or URL to a file identifying the resource to update the labels
   -h, --help[=false]: help for label
       --no-headers[=false]: When using the default output, don't print headers.
@@ -120,7 +121,7 @@ $ kubectl label pods foo bar-
 
 * [kubectl](kubectl.md)	 - kubectl controls the Kubernetes cluster manager
 
-###### Auto generated by spf13/cobra at 2015-08-26 09:03:39.977006328 +0000 UTC
+###### Auto generated by spf13/cobra at 2015-08-31 12:51:55.222410248 +0000 UTC
 
 <!-- BEGIN MUNGE: GENERATED_ANALYTICS -->
 [![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/docs/user-guide/kubectl/kubectl_label.md?pixel)]()

pkg/kubectl/cmd/label.go

@@ -90,6 +90,8 @@ func NewCmdLabel(f *cmdutil.Factory, out io.Writer) *cobra.Command {
 	cmd.Flags().String("resource-version", "", "If non-empty, the labels update will only succeed if this is the current resource-version for the object. Only valid when specifying a single resource.")
 	usage := "Filename, directory, or URL to a file identifying the resource to update the labels"
 	kubectl.AddJsonFilenameFlag(cmd, &options.Filenames, usage)
+	cmd.Flags().Bool("dry-run", false, "If true, only print the object that would be sent, without sending it.")
+
 	return cmd
 }
 
@@ -219,22 +221,31 @@ func RunLabel(f *cmdutil.Factory, out io.Writer, cmd *cobra.Command, args []stri
 		if err != nil {
 			return err
 		}
-		obj, err := cmdutil.UpdateObject(info, func(obj runtime.Object) error {
-			err := labelFunc(obj, overwrite, resourceVersion, lbls, remove)
+
+		var outputObj runtime.Object
+		if cmdutil.GetFlagBool(cmd, "dry-run") {
+			err = labelFunc(info.Object, overwrite, resourceVersion, lbls, remove)
+			if err != nil {
+				return err
+			}
+			outputObj = info.Object
+		} else {
+			outputObj, err = cmdutil.UpdateObject(info, func(obj runtime.Object) error {
+				err := labelFunc(obj, overwrite, resourceVersion, lbls, remove)
+				if err != nil {
+					return err
+				}
+				return nil
+			})
 			if err != nil {
 				return err
 			}
-			return nil
-		})
-		if err != nil {
-			return err
 		}
-
 		outputFormat := cmdutil.GetFlagString(cmd, "output")
 		if outputFormat == "" {
 			cmdutil.PrintSuccess(mapper, false, out, info.Mapping.Resource, info.Name, "labeled")
 		} else {
-			f.PrintObject(cmd, obj, out)
+			return f.PrintObject(cmd, outputObj, out)
 		}
 		return nil
 	})