title: How to grep for the dollar symbol ($)?
body: <pre><code>% cat temp
  $$$ hello1
  $$  hello2
      hello3
  ##  hello4
      hello5 $$$
  % cat temp | grep "$$$"
  Illegal variable name.
  % cat temp | grep "\$\$\$"
  Variable name must contain alphanumeric characters.
  %
  </code></pre>
  
  <p>I want to grep for <code>$$$</code> and I expect the result to be</p>
  
  <pre><code>% cat temp | grep &lt;what should go here?&gt;
  $$$ hello1
      hello5 $$$
  %
  </code></pre>
  
  <p>To differentiate, I have marked the prompt as <code>%</code>.</p>
  
  <ul>
  <li>What is the problem here?</li>
  <li>What should the <strong>grep string</strong> be?</li>
  </ul>