title: regex that matches any positive or negative numeric value but no characters or mixed strings
body: <p>I haven't used regular expressions till now, but I need a regex that matches a string representing a positive or negative numeric value like</p>
  
  <p>234</p>
  
  <p>-8</p>
  
  <p>3.346</p>
  
  <p>-564.4</p>
  
  <p>It should NOT match any text or mixtures of characters (&lt;>#?_...), numbers and text like</p>
  
  <p>abc</p>
  
  <p>.-.</p>
  
  <p>&lt;11.45</p>
  
  <p>amount111.43</p>
  
  <p>345.654.33</p>