title: Regex: How to match all strings that start with one underscore and print them without the underscore?
body: <p>My regex so far is <code>(?&lt;=_)[a-zA-Z0-9]+\b</code></p>
  <p>The input text is:</p>
  <pre><code>Calculate the _area of the _perfectRectangle object.
  
  The _id and _age variables are both integers.
  
  __invalidVariable _evenMoreInvalidVariable_ _validVariable
  </code></pre>
  <p>The output should be:</p>
  <pre><code>area,perfectRectangle
  
  id,age
  
  validVariable
  </code></pre>
  <p>But instead is:</p>
  <pre><code>area,perfectRectangle
  
  id,age
  
  invalidVariable,validVariable
  </code></pre>
  <p>How to match strings that start with only 1 underscore?<a href="https://i.stack.imgur.com/1qlE3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1qlE3.png" alt="enter image description here" /></a></p>