title: Grafana regex for transformation
body: <p>I'd like to use grafana to filter values by name:</p>
  <p>This is an example of my keys and values:</p>
  <pre><code>disk_usage.root.dev.used 0 1608582030
  disk_usage.root.dev.avail 7816 1608582030
  disk_usage.root.dev.used_percentage 0 1608582030
  disk_usage.root.run.used 147 1608582030
  disk_usage.root.run.avail 1420 1608582030
  disk_usage.root.run.used_percentage 10 1608582030
  disk_usage.root.used 6930 1608582030
  disk_usage.root.avail 214260 1608582030
  disk_usage.root.used_percentage 4 1608582030
  disk_usage.root.boot.efi.used 1 1608582030
  disk_usage.root.boot.efi.avail 120 1608582030
  disk_usage.root.boot.efi.used_percentage 1 1608582030
  </code></pre>
  <p>Now would like to show only those, whose name contains &quot;_percentage&quot;.</p>
  <p>I tried to use this:</p>
  <pre><code>/(_percentage)/
  </code></pre>
  <p>but this does not work.</p>
  <p>However, if I do the negative lookup like</p>
  <pre><code>^((?!percentage).)*$
  </code></pre>
  <p>it shows all values - but not the ones, having &quot;percentage&quot; in it.</p>
  <p>My question: How can I only show those values having &quot;percentage&quot; in it?</p>