title: Regex with blank characters
body: <p>I am trying to write a regular expression that matches the a string with the following properties: </p>
  
  <ol>
  <li>Contains exactly 3 characters.</li>
  <li>Can contain blank spaces.</li>
  <li>At least one character should be non blank space.</li>
  <li>Only blank spaces and digits are allowed.</li>
  </ol>
  
  <p>See examples below. I am using <code>b</code> to represent a blank space character.</p>
  
  <p><strong>Valid examples</strong></p>
  
  <pre>
  123
  b12
  bb1
  1bb
  12b
  </pre>
  
  <p><strong>Invalid examples</strong></p>
  
  <pre>
  bbb
  1b2
  </pre>
  
  <p>I've tried</p>
  
  <pre><code> [0-9 ]{1, 3}
  </code></pre>
  
  <p>The above regular expression matches strings with all characters blank. Can someone help me with writing a better regular expression?</p>