title: Find the first occurrence of matching regex after the first occurrence of another regex has been found
body: <p>My file looks like this </p>
  
  <pre><code>#Default GitHub
  Host github.com
    #Username username2
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_rsa_username2
  
  Host github-username1
    #Username username1
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_rsa_username1
  </code></pre>
  
  <p>I'd like to find the first username after <code>github.com</code> so it would return in this case, <code>username2</code>.</p>