$var = $_GET['data'];

If the ‘data’ parameter is not defined the expression will generate an error.

Notice: Undefined index: data in /var/www/test.php on line 9

You can hide the error using the silence @-operator.

$var = @  $_GET['data'];

Although quite useful at some times, using the @-operator can have some annoying side effects. Say you are using some external libraries in your application which uses the @-operator. If everything works fine than good. But if the library is generating some errors than it becomes difficult to point the exact location where the error occurs, as the @-operator hides it. If the external library is large, it becomes a headache to remove all the @ from the code. One nice option I found is the Scream Pecl extension. The extension allows you to easily disable the @-operator in your code without making any actual changes to the code.

Installing the Scream extension

As a pre-complied binary is not available, you need to make it yourself. The following shows commands to compile the extension on Ubuntu.

First you need to install the Pear distribution environment.

sudo apt-get install php-pear

Next you will need to install the php5-dev package to get the required PHP5 source files to compile additional modules.

sudo apt-get install php5-dev

Finally we are ready to actually create and install the extension.

sudo pecl install scream-0.1.0

Once the extension is created and installed, we need to add one to the php.ini file.

sudo gedit /etc/php5/apache2/php.ini

In the ‘extensions’ section add the following line:
extension=scream.so;

After the php.ini has been updated, you need to restart Apache, so that the new extension is loaded.

sudo /etc/init.d/apache2 restart

If hopefully all went well, the Scream extension should now be loaded, which you can confirm using phpinfo().

Breaking the Silence operator

Now you can disable the @-operator in your code using the following:

ini_set('display_errors', 1);
error_reporting(E_ALL | E_STRICT);
 
// Disable the @-operator
ini_set('scream.enabled', true);
$var = @ $_GET['data'];

Or you can directly enable the extension in your php.ini.

scream.enabled=1

Now even though the silence operator is present the above code generates an error if the ‘data’ parameter is not set. Atlast no need to hunt down for @’s while debugging.

1. Browsers Quirks – Despite the standardization in browsers, there will remain some quirks in various browsers that you will need to iron out on a regular basis.
2. Personalize Content – It may be required to deliver different type of content depending on the browser type (although it is usually not recommended); whether mobile or otherwise.
3. Illegal Access – Prevent bandwidth hogging bots and poorly programmed clients from downloading your content.

Below is a sample header for my site when using Firefox.

http://www.codediesel.com/
 
GET / HTTP/1.1
Host: www.codediesel.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.6)
Gecko/2009011913 Firefox/3.0.6 FirePHP/0.2.4
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive

PHP already has a builtin function – get_browser() that lets you determine the capabilities of the user’s browser, but it requires a browscap.ini to be installed, which sadly is not bundled with PHP, and also the function can slow down your php script. The other way to get a user agent is to use php server variables like below,

echo $_SERVER['HTTP_USER_AGENT'];

In this post we will use the Net_UserAgent_Detect Pear package to determine user agents.

Installation

Net_UserAgent_Detect being a Pear package we will use the Pear installer as below. I recommend to always use the Pear installer to download packages rather than downloading it manually as the Pear installer automatically downloads any dependent packages.

pear install Net_UserAgent_Detect-2.5.1

Usage

Usage is quite simple. For example the following code:

<?php
 
require_once 'Net/UserAgent/Detect.php';
 
echo Net_UserAgent_Detect::getUserAgent();
 
?>

will return the following string on Firefox 3.0.6: This can be quite useful if you need to log the users browser or OS type.

Mozilla/5.0 (Windows; U; Windows NT 5.1; 
en-US; rv:1.9.0.6) Gecko/2009011913 Firefox/3.0.6 FirePHP/0.2.4

getUserAgent() is only one of the many methods available in the class.

<?php
 
require_once 'Net/UserAgent/Detect.php';
 
echo('Browser String: '.Net_UserAgent_Detect::getBrowserString())."<br>";
echo('OS String: '.Net_UserAgent_Detect::getOSString())."<br>";
echo('Javascript: '.Net_UserAgent_Detect::getFeature('javascript'));
 
?>

Some other useful functions to directly test the type of browser are:
isIE()
isNavigator( )
isNetscape( )

So to detect if the user is running Firefox:

$browser = Net_UserAgent_Detect::isNetscape();