title: check for a substring in a string before the first comma
body: <p>I have a set of strings separated by <code>,</code>
  example: </p>
  
  <pre><code>abc,defg,ijkl
  
  pqrs,tu,vv
  
  ,klmnop,qwe
  
  aamn,nn,khhk
  </code></pre>
  
  <p>As you can see, the third line doesn't start with a substring. It starts with a comma.</p>
  
  <p>Using regex how can I tell a string starts with a substring of a random length  before the first comma. </p>