#!/usr/bin/perl -p -i.bak -00

s[ 	 

    	(

        < \s* A 

          \s+ HREF 

         	 \s* = \s* 

           	 ( ["'] ) 

   	 )

	    http://foo\.com/somewhere/ 

   	 (

       ( .*? ) 

        		 \2 

     .*? > 

   	 )

 ][${1}http://www.foo.com/elsewhere/$2]xsgi;