find duplicate entry in a list in bash with sed

Here I will take an example of rss2email list, but I guess I will be able to pass on the concept.

Here is example of the output of the r2e list command:

1: http://blog.amit-agarwal.co.in/feed (default: amitag@localhost)
2: http://feeds2.feedburner.com/AllAboutLinux (default: amitag@localhost)
3: http://feeds2.feedburner.com/Command-line-fu (default: amitag@localhost)
4: http://blogs.members.freewebs.com/Members/Blogs/viewBlogRSS.jsp?userid=29731143 (default: amitag@localhost)

Target here is to get the list of all duplicate entries if any. So, first we need to remove the numbers from the begining and the email ID from the end.

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<img src="http://blog.amit-agarwal.co.in/wp-content/uploads/2010/08/00_Stiqr_logo.jpg" alt="00_Stiqr_logo.jpg" width="253" height="114" align="bottom" />Ordinary <a href="http://www.makeuseof.com/tag/how-to-build-a-self-hosted-wordpress-blog-for-free/">self-hosted WordPress users know only too well that even though choosing and using thousands of available themes is a snap, creating one is an almost impossible task. You could use <a href="http://www.makeuseof.com/tag/customize-design-wordpress-theme-easily-constructor/">one of the customizable themes to modify the look to your liking, but that’s as far as you can go. Theme creating is not for the faint-hearted who are afraid to plunge into <a class="zem_slink freebase/en/html" title="HTML" rel="wikipedia" href="http://en.wikipedia.org/wiki/HTML">HTML, <a class="zem_slink freebase/en/php" title="PHP" rel="homepage" href="http://www.php.net/">PHP and <a class="zem_slink freebase/en/cascading_style_sheets" title="Cascading Style Sheets" rel="wikipedia" href="http://en.wikipedia.org/wiki/Cascading_Style_Sheets">CSS coding.

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