Add more information and options in PluginManager

New option -l, --list displays list of existing plugins
New option -h, --help displays help
Deprecate options:
   -install is now -i, --install
   -remove is now -r, --remove
   -url is now -u, --url
Catch ArraysOutOfBoundException when no arg given to install, remove or url option
Add description on plugin name structure:
- elasticsearch/plugin/version for official elasticsearch plugins (download from download.elasticsearch.org)
- groupId/artifactId/version   for community plugins (download from maven central or oss sonatype)
- username/repository          for site plugins (download from github master)
Closes #3112.

src/main/java/org/elasticsearch/plugins/PluginManager.java

@@ -288,6 +288,18 @@ public class PluginManager {
         }
     }
 
+    public void listInstalledPlugins() {
+        File[] plugins = environment.pluginsFile().listFiles();
+        System.out.println("Installed plugins:");
+        if (plugins.length == 0) {
+            System.out.println("    - No plugin detected in " + environment.pluginsFile().getAbsolutePath());
+        }
+
+        for (int i = 0; i < plugins.length; i++) {
+            System.out.println("    - " + plugins[i].getName());
+        }
+    }
+
     public static void main(String[] args) {
         Tuple<Settings, Environment> initialSettings = InternalSettingsPerparer.prepareSettings(EMPTY_SETTINGS, true);
 
@@ -298,9 +310,19 @@ public class PluginManager {
         String url = null;
         boolean verbose = false;
         for (int i = 0; i < args.length; i++) {
-            if ("url".equals(args[i]) || "-url".equals(args[i])) {
+            String command = args[i];
-                url = args[i + 1];
+            if ("-u".equals(command) || "--url".equals(command)
-            } else if ("verbose".equals(args[i]) || "-verbose".equals(args[i])) {
+                    // Deprecated commands
+                    || "url".equals(command) || "-url".equals(command)) {
+                try {
+                    url = args[i + 1];
+                } catch (Exception e) {
+                    displayHelp("Error while installing plugin, reason: " + e.getClass().getSimpleName() +
+                            ": " + e.getMessage());
+                    System.exit(1);
+                }
+            } else if ("-v".equals(command) || "--v".equals(command)
+                    || "verbose".equals(command) || "-verbose".equals(command)) {
                 verbose = true;
             }
         }
@@ -309,34 +331,69 @@ public class PluginManager {
         PluginManager pluginManager = new PluginManager(initialSettings.v2(), url);
 
         if (args.length < 1) {
-            System.out.println("Usage:");
+            displayHelp(null);
-            System.out.println("    -url     [plugin location]   : Set exact URL to download the plugin from");
-            System.out.println("    -install [plugin name]       : Downloads and installs listed plugins");
-            System.out.println("    -remove  [plugin name]       : Removes listed plugins");
-            System.out.println("    -verbose                     : Prints verbose messages");
         }
         for (int c = 0; c < args.length; c++) {
             String command = args[c];
-            if (command.equals("install") || command.equals("-install")) {
+            if (command.equals("-i") || command.equals("--install")
-                String pluginName = args[++c];
+                    // Deprecated commands
-                System.out.println("-> Installing " + pluginName + "...");
+                    || command.equals("install") || command.equals("-install")) {
+                String pluginName = null;
                 try {
+                    pluginName = args[++c];
+                    System.out.println("-> Installing " + pluginName + "...");
                     pluginManager.downloadAndExtract(pluginName, verbose);
                 } catch (IOException e) {
                     System.out.println("Failed to install " + pluginName + ", reason: " + e.getMessage());
+                } catch (Exception e) {
+                    displayHelp("Error while installing plugin, reason: " + e.getClass().getSimpleName() +
+                            ": " + e.getMessage());
+                    System.exit(1);
                 }
-            } else if (command.equals("remove") || command.equals("-remove")) {
+            } else if (command.equals("-r") || command.equals("--remove")
-                String pluginName = args[++c];
+                    // Deprecated commands
-                System.out.println("-> Removing " + pluginName + " ");
+                    || command.equals("remove") || command.equals("-remove")) {
+                String pluginName = null;
                 try {
+                    pluginName = args[++c];
+                    System.out.println("-> Removing " + pluginName + " ");
                     pluginManager.removePlugin(pluginName);
                 } catch (IOException e) {
                     System.out.println("Failed to remove " + pluginName + ", reason: " + e.getMessage());
+                } catch (Exception e) {
+                    displayHelp("Error while removing plugin, reason: " + e.getClass().getSimpleName() +
+                            ": " + e.getMessage());
                 }
+            } else if (command.equals("-l") || command.equals("--list")) {
+                pluginManager.listInstalledPlugins();
+            } else if (command.equals("-h") || command.equals("--help")) {
+                displayHelp(null);
             } else {
-                // not install or remove, continue
+                displayHelp("Command [" + args[c] + "] unknown.");
-                c++;
+                // Unknown command. We break...
+                System.exit(1);
             }
         }
     }
+
+    private static void displayHelp(String message) {
+        System.out.println("Usage:");
+        System.out.println("    -u, --url     [plugin location]   : Set exact URL to download the plugin from");
+        System.out.println("    -i, --install [plugin name]       : Downloads and installs listed plugins [*]");
+        System.out.println("    -r, --remove  [plugin name]       : Removes listed plugins");
+        System.out.println("    -l, --list                        : List installed plugins");
+        System.out.println("    -v, --verbose                     : Prints verbose messages");
+        System.out.println("    -h, --help                        : Prints this help message");
+        System.out.println();
+        System.out.println(" [*] Plugin name could be:");
+        System.out.println("     elasticsearch/plugin/version for official elasticsearch plugins (download from download.elasticsearch.org)");
+        System.out.println("     groupId/artifactId/version   for community plugins (download from maven central or oss sonatype)");
+        System.out.println("     username/repository          for site plugins (download from github master)");
+
+        if (message != null) {
+            System.out.println();
+            System.out.println("Message:");
+            System.out.println("   " + message);
+        }
+    }
 }