title: How to use sed to update the first occurrence of some text after a specified section in a file
body: <p>I have a file with the content:</p>
  
  <pre><code>#Section1
  port=3000
  port=3000
  
  #Section2
  port=3000
  port=3000
  </code></pre>
  
  <p>I want to update the first occurrence of "port=3000" to "port=1000" after the text "#Section2". Here is the output:</p>
  
  <pre><code>#Section1
  port=3000
  port=3000
  
  #Section2
  port=1000
  port=3000
  </code></pre>
  
  <p>Can anyone give me some hints about how to use sed for it? </p>
  
  <p>Thanks</p>