URL convertion from upper case to lower case

Well, you're only testing the URI value, not the host header value, so it won't matter what case is used for the hostname.

If you were going to compare hostname as well in the same fashion, you'd need to wrap it in the tolower function the same way:

if (tolower(http_uri) ends_with "/xyz" and tolower(http_host) equals "www.abc.com") {
  redirect to http://www.abc.com/pqr
}

/deb