--help: List available analyzers, improve Usage line

cmd/analyze.go

@@ -29,9 +29,11 @@ import (
 )
 
 var analyzeCmd = &cobra.Command{
-	Use:   "analyze",
-	Short: "Analyzes an image: [image]",
-	Long:  `Analyzes an image using the specifed analyzers as indicated via flags (see documentation for available ones).`,
+	Use:   "analyze image",
+	Short: "Analyzes an image: container-diff image",
+	Long: `Analyzes an image using the specifed analyzers as indicated via --type flag(s).
+
+For details on how to specify images, run: container-diff help`,
 	Args: func(cmd *cobra.Command, args []string) error {
 		if err := validateArgs(args, checkAnalyzeArgNum, checkIfValidAnalyzer); err != nil {
 			return err

cmd/diff.go

@@ -34,9 +34,11 @@ import (
 var filename string
 
 var diffCmd = &cobra.Command{
-	Use:   "diff",
-	Short: "Compare two images: [image1] [image2]",
-	Long:  `Compares two images using the specifed analyzers as indicated via flags (see documentation for available ones).`,
+	Use:   "diff image1 image2",
+	Short: "Compare two images: container-diff image1 image2",
+	Long: `Compares two images using the specifed analyzers as indicated via --type flag(s).
+
+For details on how to specify images, run: container-diff help`,
 	Args: func(cmd *cobra.Command, args []string) error {
 		if err := validateArgs(args, checkDiffArgNum, checkIfValidAnalyzer, checkFilenameFlag); err != nil {
 			return err

cmd/root.go

@@ -223,8 +223,19 @@ func (d *diffTypes) Type() string {
 }
 
 func addSharedFlags(cmd *cobra.Command) {
+	sortedTypes := []string{}
+	for analyzerType := range differs.Analyzers {
+		sortedTypes = append(sortedTypes, analyzerType)
+	}
+	sort.Strings(sortedTypes)
+	supportedTypes := strings.Join(sortedTypes, ", ")
+
 	cmd.Flags().BoolVarP(&json, "json", "j", false, "JSON Output defines if the diff should be returned in a human readable format (false) or a JSON (true).")
-	cmd.Flags().VarP(&types, "type", "t", "This flag sets the list of analyzer types to use. Set it repeatedly to use multiple analyzers.")
+	cmd.Flags().VarP(&types, "type", "t",
+		fmt.Sprintf("This flag sets the list of analyzer types to use.\n"+
+			"Set it repeatedly to use multiple analyzers.\n"+
+			"Supported types: %s.",
+			supportedTypes))
 	cmd.Flags().BoolVarP(&save, "save", "s", false, "Set this flag to save rather than remove the final image filesystems on exit.")
 	cmd.Flags().BoolVarP(&util.SortSize, "order", "o", false, "Set this flag to sort any file/package results by descending size. Otherwise, they will be sorted by name.")
 	cmd.Flags().BoolVarP(&noCache, "no-cache", "n", false, "Set this to force retrieval of image filesystem on each run.")