title: PCRE regex to sed regex
body: <p>First of all sorry for my bad english. I'm a german guy.</p>
  
  <p>The code given below is working fine in PHP:</p>
  
  <pre><code>$string = preg_replace('/href="(.*?)(\.|\,)"/i','href="$1"',$string);
  </code></pre>
  
  <p>Now T need the same for <code>sed</code>. I thought it should be:</p>
  
  <pre><code>sed 's/href="(.*?)(\.|\,)"/href="{$\1}"/g' test.htm
  </code></pre>
  
  <p>But that gives me this error:</p>
  
  <blockquote>
    <p>sed: -e expression #1, char 36:
    invalid reference \1 on `s' command's
    RHS</p>
  </blockquote>