I was recently tasked with adding Google tracking cookies to our nginx logging for a couple of sites. It was so it could be pushed through a log processor.
It turned out too be a little trickier than it would have been with Apache, but the process itself is still quite simple.
Open up the server definition you wish to add it to and add a custom log format like below
log_format g-a '$remote_addr - $remote_user [$time_local] ' '"$request" $status $body_bytes_sent ' '"$http_referer" "$http_user_agent" ' '"__utma=$cookie___utma;__utmb=$cookie___utmb;__utmc=$cookie___utmc;__utmv=$cookie___utmv;__utmz=$cookie_umtz"';
This log format can then be added to your access log like below:
access_log /var/log/nginx/access.example.com.log g-a;
sudo /etc/init.d/nginx reload
If all goes well, you should see Google Analytics appearing in your access logs like below
184.108.40.206 - - [05/Jun/2011:20:35:50 +0100] "GET / HTTP/1.1" 200 368 "" "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.1 Safari/535.1" "__utma=65957554.1846091937.1301339836.1306174686.1306258917.5;__utmb=-;__utmc=-;__utmv=-;__utmz=-"