title: Rename all files in a folder with a prefix in a single command
body: <p>Rename all the files within a folder with prefix <code>"Unix_"</code> </p>
  
  <p>Suppose a folder has two files </p>
  
  <pre><code>a.txt
  b.pdf
  </code></pre>
  
  <p>then they both should be renamed from a single command to </p>
  
  <pre><code>Unix_a.txt
  Unix_b.pdf
  </code></pre>