title: Difference between braces {} and brackets () in shell scripting
body: <p>We use braces <code>{}</code> for variable expression like</p>
  
  <pre><code>NAME="test"
  
  FILE_NAME=${NAME}file
  </code></pre>
  
  <p>But I don't understand in which scenarios we use brackets ()
  Say <code>nslookup $(hostname)</code> works only with <code>()</code> brackets.</p>
  
  <p>Can someone explain?</p>