I used this to extract referrer urls from the http server log, piping the output through deduplication, i.e. FilterInputDeletingDuplicateLines, into sort. (Or deduplicate with uniq after sorting.)

The appended variant extract-referrals emits both the referred url and its referrer.
----
 #!/usr/local/bin/scsh \
 -e main -s

 USAGE: extract-qurls.scm < INPUT > OUTPUT
 Copy quoted urls from std INPUT to std OUTPUT,
 sans quotes, line by line.

 This INPUT line
 i577B5019.versanet.de - - [18/Nov/2007:01:36:44 +0100] "GET /pix/broad.jpg HTTP/1.1" 200 11371 "http://phat.xxx/fog.html" "Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.8.1.9) Gecko/20071025 Firefox/2.0.0.9"
 would contribute the url
 http://phat.xxx/fog.html
 to the OUTPUT.
 !#

 ;; Extract (heuristically) quoted urls from (http log on) stdin
 ;; copy them (sans quotes) to stdout, line by line
 (define (extract-urls)
   (awk (read-line) (record) ()
        ((: "\""
            (submatch (: (+ alphabetic) "://" (* any)))
            "\" ")
         => (lambda (match)
                (display (match:substring match 1))
                (newline)))))


 (define (main args)
   (if (= (length args) 1)
       (extract-urls)
       (format #t "Usage: ~a < INPUT > OUTPUT~%" (first args))))

----

A variant

 ;; Extract the referred local url and its quoted referrer.
 ;; Copy them to stdout (sans quotes, separated by a tab),
 ;; line by line
 (define (extract-referrals)
   (awk (read-line) (record) ()
        ((: "GET "
            (submatch (: (+ (~ whitespace))))
            (* any)
            "\""
            (submatch (: (+ alphabetic) "://" (* any)))
            "\" ")
         => (lambda (match)
              (format #t "~a\t~a~%"
                        (match:substring match 1)
                        (match:substring match 2))
                ))))