Regex: Named Captures 

50.56.218.27 - - [13/May/2012:06:45:18 +1200] 
  "GET /path/to/page.html HTTP/1.1" 200 3635 
  "http://wellington.pm.org/source/path.html" "Mozilla/5.0"
m{^\S+ \S+ \S+ \[.*?\] "GET (/\S*) [^"]*" \d+ \d+ "\Q$site_root\E(/[^"]*)"}