title: regex exactly match the short commit id in string
body: <p>like strings lines below,  i want to match the the string which must have 1 number and letter(short commit id).</p>
  <pre><code>online-release-0202-c3764ab8-02022329     #i need c3764ab8  
  online-release-0202-02022329-c3764ab8     #i need c3764ab8
  </code></pre>
  <p>I tried the following rules, but it always matches a string of pure numbers</p>
  <pre><code>(?=([a-f0-9]{8}))
  </code></pre>