Detecting The User's Browser

Introduction

When a browser accesses any page on your website, it sends a user-agent string to the server. In PHP, this string is stored in the $_SERVER superglobals array:

$_SERVER['HTTP_USER_AGENT']

Detecting Browsers

Internet Explorer 7.0 on Vista uses this user-agent string:

Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0)

and Firefox v.2.0.0.1 uses this user-agent string:

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1

To detect a browser using Firefox, we can simply can the user-agent string for the term "firefox" since every version of Firefox since 1.0 contains this term.

To detect Internet Explorer we can use this function:

function isExplorer()
{
 if (!isset($_SERVER['HTTP_USER_AGENT'])){
  return null;
 }
	
 $agent = $_SERVER['HTTP_USER_AGENT'];
 
 if (eregi("MSIE", $agent)){
  return true;
 }
			
 return false;
}

We can further expand this code to detect other browsers if we know the various user-agent strings. For a complete list of this, Wikipedia has an extensive list

Here is a small class that will detect some popular browsers:

<?php
 
class Browser 
{
	function getPlatform()
	{
		if (!isset($_SERVER['HTTP_USER_AGENT'])){
			return null;
		}
		
		$agent = $_SERVER['HTTP_USER_AGENT'];
		
		if (eregi("win", $agent)){
			return "Windows";
		}
		
		if (eregi("mac", $agent)){
			return "Mac";
		}
		
		if (eregi("linux", $agent)){
			return "Linux";
	        }
			
		return "Unknown";
	}
	
	function isFirefox()
	{
		if (!isset($_SERVER['HTTP_USER_AGENT'])){
			return null;
		}
		
		$agent = $_SERVER['HTTP_USER_AGENT'];
		
		if (eregi("Firefox", $agent)){
			return true;
		}
		
		return false;
	}
	
	
	function isExplorer()
	{
	        if (!isset($_SERVER['HTTP_USER_AGENT'])){
			return null;
		}
		
		$agent = $_SERVER['HTTP_USER_AGENT'];
		
		if (eregi("MSIE", $agent)){
			return true;
		}
		
		return false;
	}
	
}
?>

So, to check whether the user is using firefox you would write:

<?php
 
 if (Browser::isFirefox()){
   /* your code goes here */
 }
 
?>

Now you should be able to detect the user's browser using PHP. This can be useful if you need to switch your style sheet to deal with different browsers.

Detecting The User's Browser