title: Group lines by prefix
body: <p>I have a file full of keys and values which I use for i18n. The file looks like this:</p>
  
  <pre class="lang-none prettyprint-override"><code>foo.foo=Some string
  foo.bar=Some string
  bar.foo=Some string
  bar.bar=Some string
  baz.foo=Some string
  baz.bar=Some string
  </code></pre>
  
  <p>Using some unix tool like awk or sed, how can I filter the file so that lines beginning with the same prefix (up to the first dot) are grouped together, and groups are separated by a blank line?</p>
  
  <p>The output should look like</p>
  
  <pre class="lang-none prettyprint-override"><code>foo.foo=Some string
  foo.bar=Some string
  
  bar.foo=Some string
  bar.bar=Some string
  
  baz.foo=Some string
  baz.bar=Some string
  </code></pre>