title: What is EOF!! in the bash script?
body: <p>There is a command I don't understand:</p>
  
  <pre><code>custom_command &lt;&lt; EOF!!
  </code></pre>
  
  <p>I want to ask what EOF!! is in the bash script. I did find EOF with google, but google will ignore the "!!" automatically, so I cannot find EOF!!. </p>
  
  <p>I know the end of the file token, but I don't exactly know what it means with the "!!" in the script. Is this a mark to force something to do something like in vim's wq! ?</p>
  
  <p>Plus, why and when should we use EOF!! instead of EOF?</p>