add "version" command to display git version string (#221)

* add "version" command to display git version string

* drop unused parameter

Makefile

@@ -4,7 +4,8 @@ export TFJSON?=
 export KUBEONE_CONFIG_FILE?=config.yaml.dist
 export KUBERNETES_VERSION=1.13.3
 BUILD_IMAGE?=golang:1.11.5
-GOLDFLAGS?=-w -s
+GITTAG=$(shell git describe --tags --always)
+GOLDFLAGS?=-w -s -X github.com/kubermatic/kubeone/pkg/cmd.versionString=$(GITTAG)
 
 PROVIDER=$(notdir $(wildcard ./terraform/*))
 CREATE_TARGETS=$(addsuffix -env,$(PROVIDER))

pkg/cmd/root.go

@@ -46,6 +46,7 @@ func newRoot() *cobra.Command {
 		upgradeCmd(fs),
 		resetCmd(fs),
 		kubeconfigCmd(fs),
+		versionCmd(fs),
 	)
 
 	return rootCmd

pkg/cmd/version.go

@@ -0,0 +1,26 @@
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+	"github.com/spf13/pflag"
+)
+
+var versionString = "development"
+
+// versionCmd setups version command
+func versionCmd(_ *pflag.FlagSet) *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "version",
+		Short: "Display KubeOne version",
+		Long:  `Prints the exact version number, as embedded by the build system.`,
+		Args:  cobra.ExactArgs(0),
+		RunE: func(_ *cobra.Command, args []string) error {
+			fmt.Printf("KubeOne %s\n", versionString)
+			return nil
+		},
+	}
+
+	return cmd
+}