PHP Web Concepts
This session demonstrates
how PHP can provide dynamic content according to browser type, randomly
generated numbers or User Input. It also demonstrated how the client borwser
can be redirected.
PHP creates some
useful environment variables that can be seen in the
phpinfo.php page that was used to setup the PHP environment.
One of the environemnt
variables set by PHP is HTTP_USER_AGENT which identifies the
user's browser and operating system.
PHP provides a function
getenv() to access the value of all the environment variables. The information
contained in the HTTP_USER_AGENT environment variable can be used to create
dynamic content appropriate to the borwser.
Following example
demonstrates how you can identify a client borwser and operating system.
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<html>
<body>
<?php
$viewer = getenv( "HTTP_USER_AGENT" );
$browser = "An unidentified browser";
if(
preg_match( "/MSIE/i", "$viewer" ) )
{
$browser = "Internet Explorer";
}
else
if( preg_match(
"/Netscape/i", "$viewer" ) )
{
$browser = "Netscape";
}
else
if( preg_match(
"/Mozilla/i", "$viewer" ) )
{
$browser = "Mozilla";
}
$platform = "An unidentified OS!";
if(
preg_match( "/Windows/i", "$viewer" ) )
{
$platform = "Windows!";
}
else
if ( preg_match( "/Linux/i", "$viewer" ) )
{
$platform = "Linux!";
}
echo("You are using $browser on $platform");
?>
</body>
</html>
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This is producing following
result on my machine. This result may be different for your computer depnding
on what you are using.
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You are using Mozilla! on Windows!
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The PHP rand() function
is used to generate a random number.i This function can generate numbers
with-in a given range. The random number generator should be seeded to prevent
a regular pattern of numbers being generated. This is achieved using the srand() function
that specifiies the seed number as its argument.
Following example
demonstrates how you can display different image each time out of four images:
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<html>
<body>
<?php
srand(
microtime() * 1000000 );
$num =
rand( 1, 4 );
switch( $num )
{
case
1: $image_file = "/home/images/alfa.jpg";
break;
case
2: $image_file = "/home/images/ferrari.jpg";
break;
case
3: $image_file = "/home/images/jaguar.jpg";
break;
case
4: $image_file = "/home/images/porsche.jpg";
break;
}
echo
"Random Image : <img src=$image_file />";
?>
</body>
</html>
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The most important thing to
notice when dealing with HTML forms and PHP is that any form element in an HTML
page will automatically be available to your PHP scripts.
Try out following example
by putting the source code in test.php script.
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<?php
if(
$_POST["name"] || $_POST["age"] )
{
echo "Welcome ". $_POST['name']. "<br />";
echo "You are ". $_POST['age']. " years old.";
exit();
}
?>
<html>
<body>
<form action="<?php $_PHP_SELF ?>"
method="POST">
Name:
<input type="text" name="name" />
Age:
<input type="text" name="age" />
<input
type="submit" />
</form>
</body>
</html>
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- The PHP default variable $_PHP_SELF is used for the PHP script name and when you click "submit" button then same PHP script will be called and will produce following result:
- The method = "POST" is used to post user data to the server script. There are two methods of posting data to the server script which are discussed in PHP GET & POSTchapter.
The PHP header() function
supplies raw HTTP headers to the browser and can be used to redirect it to
another location. The redirection script should be at the very top of the page
to prevent any other part of the page from loading.
The target is specified by
the Location: header as the argument to the header() function.
After calling this function the exit() function can be used to
halt parsing of rest of the code.
Following example
demonstrates how you can redirect a borwser request to another web page. Try
out this example by puttingthe source code in test.php script.
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<?php
if(
$_POST["location"] )
{
$location = $_POST["location"];
header( "Location:$location" );
exit();
}
?>
<html>
<body>
<p>Choose a site to visit :</p>
<form action="<?php $_PHP_SELF ?>"
method="POST">
<select name="location">
<option value="http://w3c.org">
World Wise Web Consortium
</option>
<option value="http://www.google.com">
Google Search Page
</option>
</select>
<input type="submit" />
</form>
</body>
</html>
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Sometime it is desired that
you want to give option where a use will click a link and it will pop up a
"File Download" box to the user in stead of displaying actual
content. This is very easy and will be achived through HTTP header.
The HTTP header will be
different from the actual header where we send Content-Type astext/html\n\n.
In this case content type will be application/octet-stream and
actual file name will be concatenated along with it.
For example, if you want
make a FileName file downloadable from a given link then its
syntax will be as follows.
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#!/usr/bin/perl
# HTTP Header
print "Content-Type:application/octet-stream;
name=\"FileName\"\r\n";
print "Content-Disposition:
attachment; filename=\"FileName\"\r\n\n";
# Actual File Content
open( FILE, "<FileName" );
while(read(FILE, $buffer, 100) )
{
print("$buffer");
}
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