title: How do I replace a substring of a string before a specific character?
body: <p>Table <code>Email</code>:</p>
  
  <p>Values:</p>
  
  <pre><code>josh@yahoo.com
  carmine32@hotmail.com
  zehmaneh@yahoo.com
  </code></pre>
  
  <p>I want to replace the string before <code>@</code> with <code>test</code>.</p>
  
  <p>Result:</p>
  
  <pre><code>test@yahoo.com
  test@hotmail.com
  test@yahoo.com
  </code></pre>
  
  <p>How do I use substringing and replace based on a character in the string?</p>