title: Regular Expression in R for twitter username
body: <p>I am looking to handle and text between <strong>@</strong> and <strong>:</strong> with out any space for example 
  @rstat:.
  I would like to form a regular expression to handle this.
  I have tried <strong>^@.[A-z0-9_].:$</strong> but its not working.</p>
  
  <p>Kindly help me here.</p>