title: Find and replace using regex in sed
body: <p>I want to replace</p>
  
  <pre><code># Bulk Delete #
  </code></pre>
  
  <p>with </p>
  
  <pre><code>=== Bulk Delete ===
  </code></pre>
  
  <p>I am using the following <code>sed</code> command. </p>
  
  <pre><code>sed "s/#\([^#]*\)#/===\1===/g" filename
  </code></pre>
  
  <p>It works, but it also replaces</p>
  
  <pre><code>### Translation
  </code></pre>
  
  <p>with</p>
  
  <pre><code>======# Translation
  </code></pre>
  
  <p>How to prevent it and make it work in both mac and ubuntu?</p>