title: What does sed -i option do?
body: <p>I'm debugging a shell script and trying to find out the task performed by the following command:</p>
  
  <pre><code>sed -i '1,+999d' /home/org_user/data.txt
  </code></pre>
  
  <p>I need to change this command as its failing with the following error:</p>
  
  <pre><code>illegal option sed -i
  </code></pre>
  
  <p>But before changing, I need to understand the BAU functioning.</p>
  
  <p>Appreciate any inputs in this regard.</p>