title: How to replace to apostrophe ' inside a file using SED
body: <p>I have a file "test.txt" that contain the following</p>
  
  <pre><code>+foo+
  +bar+
  </code></pre>
  
  <p>What I want to do is to replace them into:</p>
  
  <pre><code>'foo'
  'bar'
  </code></pre>
  
  <p>But why this code doesn't work?</p>
  
  <pre><code>sed  's/\+/\'/' test.txt
  </code></pre>
  
  <p>What's the right way to do it?</p>