title: How to transform multiple line into one line in bash stdout?
body: <p>I sometimes do this in my shell :</p>
  
  <pre><code>sam@sam-laptop:~/shell$ ps aux | grep firefox | awk '{print $2}'
  2681
  2685
  2689
  4645
  
  $ kill -9 2681 2685 2689 4645
  </code></pre>
  
  <p>Is there a way I can transform the multiple lines containing the PIDs into one line separated by spaces ?
  (It's a little bit annoying to type the PIDs every time and I really would like to learn :) )</p>
  
  <p>Thanks a lot.</p>