title: Looking for a Perl or sed one-liner to replace a string with contents from another file
body: <p>In an HTML file, let’s call it <code>index.html</code>, I want to replace a comment string, say <code>//gac goes here</code>, with the contents (multi-line) from a separate file which is called: gac.js. Is there a nice one-liner for that?</p>
  
  <p>I found something as: <code>sed -e "/$str/r FileB" -e "/$str/d" FileA</code>, but it is not working as promised.</p>
  
  <p>I do like it as short as possible, as it will be called after an <a href="http://en.wikipedia.org/wiki/Apache_Subversion" rel="nofollow">SVN</a> revert (I don't want any of that google.script polluting my development environment).</p>