title: Regex math a string only contain two words in Elixir
body: <p>I want to match a string to contain <strong>only</strong> two words, like a <code>user:passwd</code> format, my suggesting is </p>
  
  <pre><code>Regex.match?(%r/^\w:\w$/, string)
  </code></pre>
  
  <p>But it doesn't works.... Could someone helps me? </p>
  
  <p>I want these examples to match: <code>a:b</code> <code>aa:23bw</code>;</p>
  
  <p>and these examples not to match: <code>a: b</code>, <code>a:b  c</code></p>