feat: add version command

cmd/root.go

@@ -4,11 +4,15 @@ import (
 	"github.com/spf13/cobra"
 )
 
+const (
+	ProgramName = "dockerfile-image-tags"
+)
+
 var (
 	unknownMarker string
 
 	rootCmd = &cobra.Command{
-		Use:   "dockerfile-image-tags",
+		Use:   ProgramName,
 		Short: "List or query images and tags used in a Dockerfile.",
 	}
 )

cmd/version.go

@@ -0,0 +1,34 @@
+package cmd
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+var Version = "development"
+var Revision = ""
+
+var (
+	versionCmd = &cobra.Command{
+		Use:   "version",
+		Short: "Prints version",
+		Long:  "Prints the program’s version information.",
+		Args:  cobra.ExactArgs(0),
+		Run: func(cmd *cobra.Command, args []string) {
+			git := ""
+			r := strings.TrimSpace(Revision)
+
+			if len(r) > 0 {
+				git = fmt.Sprintf(" (r%s)", r)
+			}
+
+			fmt.Printf("%s %s%s", ProgramName, Version, git)
+		},
+	}
+)
+
+func init() {
+	rootCmd.AddCommand(versionCmd)
+}