title: ruby on rails replace some string
body: <p>I have two strings. One is:</p>
  
  <p><code>"/system/musics/videos/000/000/001/original/%E5%B9%BF%E5%9C%BA%E8%88%9E%E5%BF%AB%E5%9B%9B_-_%E5%A4%A7%E8%8D%89%E5%8E%9F-%E4%BE%AF%E6%AD%8C.MP3"
  </code></p>
  
  <p>The second one is:</p>
  
  <pre><code>"广场舞快四_-_大草原-侯歌.MP3"
  </code></pre>
  
  <p>I want to get:</p>
  
  <pre><code>"/system/musics/videos/000/000/001/original/广场舞快四_-_大草原-侯歌.MP3"
  </code></pre>
  
  <p>Does anyone know how to find and replace the string in ruby? My idea is to replace the contents after the last <code>'/'</code> with the second string. How can I do it?</p>