adding the missing classes to show the real purpose of the pattern

Command/Invoker.php

@@ -0,0 +1,34 @@
+<?php
+
+/*
+ * DesignPatternPHP
+ */
+
+namespace DesignPatterns\Command;
+
+/**
+ * Invoker is using the command given to it.
+ * Example : an Application in SF2
+ */
+class Invoker
+{
+
+    protected $command;
+
+    /**
+     * In the invoker we find this kind of method for subscribing the command.
+     * There can be also a stack, a list, a fixed set...
+     */
+    public function setCommand(Command $cmd)
+    {
+        $this->command = $cmd;
+    }
+
+    public function run()
+    {
+        // here is a key feature of the invoker
+        // the invoker is the same whatever is the command
+        $this->command->execute();
+    }
+
+}