Modify one part of URI Path

[root@ve10:Active] config  b virtual bar list
virtual bar {
   snat automap
   pool foo
   destination 172.28.19.79:80
   ip protocol 6
   rules myrule
   profiles {
      http {}
      tcp {}
   }
}
[root@ve10:Active] config  b class foo_class list
class foo_class {
   "/dir2/" { "/dir1/ /dir5/" }
}
[root@ve10:Active] config  b rule myrule list
rule myrule {
   when HTTP_REQUEST {
   if { [class match -- [HTTP::uri] contains foo_class] } {
      set uri [string map [class match -value [HTTP::uri] contains foo_class] [HTTP::uri]]
      HTTP::redirect "http://[HTTP::host]$uri"
   }
}
}

[root@ve10:Active] config  curl -I "http://172.28.19.79/dir1/dir2/file.ext?arg1=val1&arg2=val2&arg3"
HTTP/1.0 302 Found
Location: http://172.28.19.79/dir5/dir2/file.ext?arg1=val1&arg2=val2&arg3
Server: BigIP
Connection: Keep-Alive
Content-Length: 0

[root@ve10:Active] config  curl -I "http://172.28.19.79/somethingelse/file.ext?arg1=val1&arg2=val2&arg3"
HTTP/1.1 404 Not Found
Date: Wed, 24 Oct 2012 00:18:48 GMT
Server: Apache/2.2.3 (CentOS)
Connection: close
Content-Type: text/html; charset=iso-8859-1