title: Remove new line / line break characters only for specific lines
body: <p>I have the following output:</p>
  
  <pre><code>02:01:31
  OFFLINE
  02:02:31
  ONLINE
  </code></pre>
  
  <p>and I would like it to become:</p>
  
  <pre><code>02:01:31 OFFLINE
  02:02:31 ONLINE
  </code></pre>
  
  <p>I found a way of removing all newline / line breaks with <code>sed ':a;N;$!ba;s/\n/ /g'</code> however  it gives me what follows which is not really what I'm after:</p>
  
  <pre><code>02:01:31 OFFLINE 02:02:31 ONLINE
  </code></pre>
  
  <p><strong>Q: How can I remove newline / line breaks only for lines that match a certain pattern (in this case <code>[0-9]</code> would be enough?</strong></p>
  
  <p>PS: It doesn't have to be with <code>sed</code> as long as I can apply a regex pattern to the matching of lines</p>