title: Regular expression for one character only
body: <p>I need a regular expression for a string with exactly one alphabetic character in it.</p>
  
  <p>For example, it should match:</p>
  
  <ul>
  <li><code>8*x=16</code></li>
  <li><code>x+2=2</code></li>
  <li><code>u329398239823</code></li>
  <li><code>43044343k43304403</code></li>
  </ul>
  
  <p>...but not:</p>
  
  <ul>
  <li><code>xsfdjfefljefe</code></li>
  <li><code>44434f9434343 f</code></li>
  <li><code>98(***(*)))(*)(0((-900-87</code></li>
  <li><code>32233232</code></li>
  </ul>