title: Validate Mobile number using regular expression
body: <p>I need to validate mobile number. My need:</p>
  
  <blockquote>
    <ol>
    <li>The number may start with +8801 or 8801 or 01</li>
    <li>The next number can be 1 or 5 or 6 or 7 or 8 or 9</li>
    <li>Then there have exact 8 digit.</li>
    </ol>
  </blockquote>
  
  <p>How can i write the regular expression using this conditions ?</p>
  
  <p>the mobile numbers I tried</p>
  
  <pre><code>+8801811419556
  01811419556
  8801711419556
  01611419556
  8801511419556
  </code></pre>