title: Select line matching pattern +1
body: <p>How do I use <em>sed</em> to select every line matching a pattern + the next line?
  For instance, I'd like to select all lines with <em>tag=&quot;foo&quot;</em> plus the next line.
  As an alternative, I'd also like to be able to select lines with <em>tag=&quot;foo&quot;</em> OR <em>group=&quot;bar&quot;</em> plus the next line.</p>