title: How can I get the current plugin directory in WordPress?
body: <p>I need to get the current plugin directory like:</p>
  <pre><code>[wordpress_install_dir]/wp-content/plugins/plugin_name
  </code></pre>
  <p>(If <code>getcwd()</code> is called from the plugin, it returns <code>[wordpress_install_dir]</code>, the root of installation.)</p>