title: Regex - Renaming files with a prefix/suffix
body: <p>Command below is from this answer: <a href="https://stackoverflow.com/a/208220/3470343">https://stackoverflow.com/a/208220/3470343</a></p>
  
  <p>The command adds the word <code>new.</code> as a prefix. That's understood.</p>
  
  <pre><code>rename 's/(.*)$/new.$1/' original.filename
  </code></pre>
  
  <p>However, I'd like to ask why the open and close brackets are required here:</p>
  
  <pre><code>(.*)
  </code></pre>
  
  <p>And also why is <code>$1</code> the variable which stores the original file name, why can't I do the the same with following (where i have replaced <code>$1</code> with <code>$2</code>):</p>
  
  <pre><code>rename 's/(.*)$/new.$2/' original.filename
  </code></pre>
  
  <p>I'm still relatively new to bash, so help would be greatly appreciated.</p>