Add Google Analytics tracking code to HTML via nginx

analytics.conf

#
# Add Google Analytics tracking code to HTML response
#
# Usage:
#   set $tracking_id 'UA-12345678-9';
#   include incl/analytics.conf;
#
# It needs nginx compiled with option --with-http_sub_module.
# Uses optimized GA code from: http://mathiasbynens.be/notes/async-analytics-snippet
#
sub_filter '</head>' '<script type="text/javascript">var _gaq=[["_setAccount","$tracking_id"],["_trackPageview"]];(function(d,t){var g=d.createElement(t),s=d.getElementsByTagName(t)[0];g.async=1;g.src="//www.google-analytics.com/ga.js";s.parentNode.insertBefore(g,s)})(document,"script")</script></head>';