reliable user browser detection with php

Question

Trying to detect a user's browser with PHP only, is $_SERVER['HTTP_USER_AGENT'] a reliable way? Should I instead opt for the get_browser function? which one do you find brings more precise results?

If this method is pragmatic, is it ill advised to use it for outputting pertinent CSS links, for example:

if(stripos($_SERVER['HTTP_USER_AGENT'],"mozilla")!==false)    echo '<link type="text/css" href="mozilla.css" />'; 

I noticed this question, however I wanted to clarify whether this is good for CSS-oriented detection.

UPDATE: something really suspicious: I tried echo $_SERVER['HTTP_USER_AGENT']; on IE 7 and this is what it output:

Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; SLCC1; .NET CLR 2.0.50727; Media Center PC 5.0; .NET CLR 3.5.30729; .NET CLR 3.0.30618)

Safari gave something weird with "mozilla" in it too. What gives?

Answer 1

Check this code , I've found this is useful. Don't check Mozilla because most browser use this as user agent string

if(strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== FALSE)    echo 'Internet explorer';  elseif(strpos($_SERVER['HTTP_USER_AGENT'], 'Trident') !== FALSE) //For Supporting IE 11     echo 'Internet explorer';  elseif(strpos($_SERVER['HTTP_USER_AGENT'], 'Firefox') !== FALSE)    echo 'Mozilla Firefox';  elseif(strpos($_SERVER['HTTP_USER_AGENT'], 'Chrome') !== FALSE)    echo 'Google Chrome';  elseif(strpos($_SERVER['HTTP_USER_AGENT'], 'Opera Mini') !== FALSE)    echo "Opera Mini";  elseif(strpos($_SERVER['HTTP_USER_AGENT'], 'Opera') !== FALSE)    echo "Opera";  elseif(strpos($_SERVER['HTTP_USER_AGENT'], 'Safari') !== FALSE)    echo "Safari";  else    echo 'Something else';