title: Why doesn't this regex work with Ruby
body: <p>Trying to to match the hash character fails, but succeeds for any other member 
  of the regex.</p>
  
  <p>Why does this fail?</p>
  
  <p>Thanks,</p>
  
  <p>Joe</p>
  
  <pre><code>UNIT = [ 'floor', 'fl', '#', 'penthouse', 'mezzanine', 'basement', 'room' ]
  
  unit_regex = "\\b(" + UNIT.to_a.join("|") + ")\\b"
  
  unit_regexp = Regexp.new(unit_regex, Regexp::IGNORECASE)
  
  x=unit_regexp.match('#')
  </code></pre>