title: tcl variable sql injection check
body: <p>I have a tcl variable $value that is being passed through a hidden input field.
  What would be a good regular expression to get it checked for an SQL injection.</p>
  
  <p>I would want it to allow only numbers in case.</p>
  
  <p>I would want it to allow only characters in another case.</p>
  
  <p>And numbers and characters both in another case.</p>
  
  <p>In all 3  cases I do not want any special chracters to be included</p>