title: Password validation with regexp
body: <p>I am trying to write password validation function with regexp and don't know how to do it.</p>
  <p>The regex package provided by the standard API of the Go language is different to other languages.</p>
  <p>Have someone an idea, how this regexp pattern should looks like?</p>
  <p>The pattern should validate:</p>
  <pre><code>/*
   * Password rules:
   * at least 7 letters
   * at least 1 number
   * at least 1 upper case
   * at least 1 special character
   */
  </code></pre>