Add Google Analytics tracking code to HTML via nginx

analytics.nginx

# Add Google Analytics tracking code to HTML response
#
# Usage:
#   set $tracking_id 'UA-********-*';
#   include incl/analytics.conf;
#
# It needs nginx compiled with option --with-http_sub_module.
# Uses optimized GA code from: http://mathiasbynens.be/notes/async-analytics-snippet
#
sub_filter </head> "<script>(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)})(window,document,'script','https://www.google-analytics.com/analytics.js','ga');ga('create', '$tracking_id', 'auto');ga('send', 'pageview');</script></head>";