title: Bash - how to append a newline after lines starting with the same letter?
body: <p>I have a file with, let's say, the following lines:</p>
  
  <pre><code>alibi
  all
  bone
  chair
  clever
  cup
  curse
  dog
  donut
  </code></pre>
  
  <p>I want to add a newline after the last word that starts with the same letter; that is, I want the output to be:</p>
  
  <pre><code>alibi
  all
  
  bone
  
  chair
  clever
  cup
  curse
  
  dog
  donut
  </code></pre>
  
  <p>Is there any way to do it? I'm not an expert so I don't even know where to start for this one. I prefer it to be a one-liner, too.</p>
  
  <p>I'm working in Windows environment Cygwin.</p>