title: Php file_exist with regex
body: <p>I am trying to use regex pattern to search for files.</p>
  
  <p>Directory path is:</p>
  
  <pre><code>$css_dir = MY_PLUGIN_DIR.'/source/css/';
  </code></pre>
  
  <p>Css filename starts with:</p>
  
  <pre><code>$css_prefix = 'hap_css_';
  </code></pre>
  
  <p>and ends with:</p>
  
  <pre><code>'.css'
  </code></pre>
  
  <p>With some amount of unknown characters in between.</p>
  
  <p>I dont know how to construct regex pattern with variable and how to construct file exist with regex.</p>
  
  <p>Thank you!</p>