title: Build list of substrings created by separating a string by a match
body: <p>I have a string:</p>
  
  <pre><code>"a_b_c_d_e"
  </code></pre>
  
  <p>I would like to build a list of substrings that result from removing everything after a single <code>"_"</code> from the string. The resulting list would look like:</p>
  
  <pre><code>['a_b_c_d', 'a_b_c', 'a_b', 'a']
  </code></pre>
  
  <p>What is the most rubyish way to achieve this?</p>