title: how can I find two consecutive lines having the the same pattern
body: <p>My text files looks like that:</p>
  
  <pre><code>bla : 1 - etc
  blb : a - etc
  blc : 2 - etc
  bld : 3 - etc
  ble : 1 - etc
  blf : 1 - etc
  blg : a - etc
  blh : 1 - etc
  bli : a - etc
  </code></pre>
  
  <p>I am searching for the pattern <code>": 1 -"</code> in the file. Some consecutive lines have the same pattern and I need these two lines plus the next line.</p>
  
  <pre><code>ble : 1 - etc
  blf : 1 - etc
  blg : a - etc
  </code></pre>
  
  <p>Is it possible to extract this lines with <code>grep</code>, <code>sed</code> or any other tool?
  Thanks in advance.</p>