title: Match a content with regexp in a file?
body: <p>I want to see if a text already is in a file using regexp.</p>
  
  <pre><code># file.txt
  Hi my name is Foo
  and I live in Bar
  and I have three children.
  </code></pre>
  
  <p>I want to see if the text:</p>
  
  <pre><code>Hi my name is Foo
  and I live in Bar
  </code></pre>
  
  <p>is in this file.</p>
  
  <p>How can I match it with a regexp?</p>