title: sed replace two open brackets with a single one
body: <p>I have a file containing lines like</p>
  
  <pre><code>echo ((hello world))
  </code></pre>
  
  <p>I want the output to be</p>
  
  <pre><code> echo (hello world)
  </code></pre>
  
  <p>Any idea how I can accomplish this with sed?</p>
  
  <pre><code>sed  's/echo \(\(/echo \(\/' myfile
  </code></pre>
  
  <blockquote>
    <p>sed: -e expression #1, char 21: unterminated `s' command</p>
  </blockquote>