title: Check if string contains an underscore in PHP
body: <p>I'm was wondering of a lightweight way of finding if a string contains an underscore (_).
  As a bonus if it was possible to have an if statement that not only checks for an underscore checks if the string is only <strong>two words</strong> connected.</p>
  
  <p><strong>E.g</strong> I'm looking to check for strings like this "foo_bar".</p>
  
  <p>With no spaces, just the two words and an underscore.</p>
  
  <p>Any help would be great,</p>
  
  <p>Thanks!</p>