Davor Josipovic Just another WordPress blog – rather tryout


Google Analytics on-the-fly insertion with Apache

Filed under: php,Programming — Tags: , — Davor @ 22:46

I recently needed to insert the Google Analytics script on the fly on each html page that an Apache server was sending. Kirill Minkovich has made a good overview of the standard ways for doing so. Particularly the second and third solutions are interesting because they use the ext_filter_module which is meant for such things.

External filters are slow. Since Apache 2.2.7 there is a internal SUBSTITUTE filter.

AddOutputFilterByType SUBSTITUTE text/html
Substitute "s#<head(.*)>#<head$1>\
    <!-- Global site tag (gtag.js) - Google Analytics -->\
    <script async src=\"https://www.googletagmanager.com/gtag/js?id=UA-19913980-1\"></script>\
       window.dataLayer = window.dataLayer || [];\
       function gtag(){dataLayer.push(arguments);}\
       gtag('js', new Date());\
       gtag('config', 'UA-XXXXXXX-X');\

That’s it! Make sure that DEFLATE filter is not run before, otherwise the SUBSTITUTE filter will get a gzipped stream and thus will not be able to insert the code.

Note: Aaron Gloege also has a very interesting php-only solution for this problem, but I, IMHO, thought it a bit farfetched. Nonetheless, it is probably (much) faster than the one used below.

Here is a simpler version for the filter.google-analytics.php file:

$ga_script =
"<script type=\"text/javascript\">
  var _gaq = _gaq || [];
  _gaq.push(['_setAccount', 'UA-XXXXXXXX-X']);
  (function() {
    var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
    ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
    var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
$handle = fopen ("php://stdin","r");
// Will read the whole stream. 
// Use $sHtmlFile = fgets($handle); for testing purposes from command line.
$sHtmlFile = stream_get_contents($handle);
// We allow only one replacement before one of the 3 tags.
// From testing it appears that php PCRE engine replaces the
// first match from the stream. So the ga_script will probably
// be inserted before </head> as Google recommends.
$sHtmlFile = preg_replace(
if ($replacements == 0)
	$sHtmlFile = $sHtmlFile . $ga_script;
echo $sHtmlFile;

And of course, add the following to your apache.conf file:

LoadModule ext_filter_module modules/mod_ext_filter.so
ExtFilterDefine insert-google-analytics cmd="/bin/php /cgi-bin/filter.google-analytics.php" mode=output
AddOutputFilter insert-google-analytics htm html

Powered by WordPress