title: Sed command find and replace in even lines of a file
body: <p>Hi I am new to this forum. I want to use SED to replace an expression on even lines of a file. My problem is that I cannot think f how to save the changes in the original file (i.e, how to overwrite the changes in the file). I have tried with :</p>
  
  <pre><code>sed -n 'n;p;' filename | sed 's/aaa/bbb/'
  </code></pre>
  
  <p>but this does not save the changes. I appreciate your help on this.     </p>