The PHP Hypertext Preprocessor (PHP) is a programming language that allows web developers to create dynamic content that interacts with databases. PHP is a general-purpose scripting language geared towards web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1994. PHP is an open-source, interpreted, and object-oriented scripting language that can be executed at the server-side.
- PHP files can contain text, HTML, CSS, JavaScript, and PHP code
- PHP code is executed on the server, and the result is returned to the browser as plain HTML
- PHP files have extension “
.php“
What Can PHP Do?
- PHP can generate dynamic page content
- PHP can create, open, read, write, delete, and close files on the server
- PHP can collect form data
- PHP can send and receive cookies
- PHP can add, delete, modify data in your database
- PHP can be used to control user-access
- PHP can encrypt data
With PHP you are not limited to output HTML. You can output images, PDF files, and even Flash movies. You can also output any text, such as XHTML and XML.
Why PHP?
- PHP runs on various platforms (Windows, Linux, Unix, Mac OS X, etc.)
- PHP is compatible with almost all servers used today (Apache, IIS, etc.)
- PHP supports a wide range of databases
- PHP is free. Download it from the official PHP resource: www.php.net
- PHP is easy to learn and runs efficiently on the server side
What Do I Need?
To start using PHP, you can:
- Find a web host with PHP and MySQL support
- Install a web server on your own PC, and then install PHP and MySQL
A PHP script is executed on the server, and the plain HTML result is sent back to the browser.
Basic PHP Syntax
A PHP script can be placed anywhere in the document.
A PHP script starts with <?php and ends with ?>:
<?php
// PHP code goes here
?>
The default file extension for PHP files is “.php“.
A PHP file normally contains HTML tags, and some PHP scripting code.
Below, we have an example of a simple PHP file, with a PHP script that uses a built-in PHP function “echo” to output the text “Hello World!” on a web page:
Example
<!DOCTYPE html>
<html>
<body>
<h1>My first PHP page</h1>
<?php
echo “Hello World!”;
?>
</body>
</html>
Note: PHP statements end with a semicolon (;).
PHP Case Sensitivity
In PHP, keywords (e.g. if, else, while, echo, etc.), classes, functions, and user-defined functions are not case-sensitive.
In the example below, all three echo statements below are equal and legal:
Example
<!DOCTYPE html>
<html>
<body>
<?php
ECHO “Hello World!<br>”;
echo “Hello World!<br>”;
EcHo “Hello World!<br>”;
?>
</body>
</html>
PHP Variables
Variables are “containers” for storing information.
Creating (Declaring) PHP Variables
In PHP, a variable starts with the $ sign, followed by the name of the variable:
Example
<?php
$txt = “Hello world!”;
$x = 5;
$y = 10.5;
?>
PHP Variables
A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume).
Rules for PHP variables:
- A variable starts with the
$sign, followed by the name of the variable - A variable name must start with a letter or the underscore character
- A variable name cannot start with a number
- A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
- Variable names are case-sensitive (
$ageand$AGEare two different variables)
Remember that PHP variable names are case-sensitive!
PHP Variables Scope
In PHP, variables can be declared anywhere in the script.
The scope of a variable is the part of the script where the variable can be referenced/used.
PHP has three different variable scopes:
- local
- global
- static
Global and Local Scope
A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function:
Example
Variable with global scope:
<?php
$x = 5; // global scope
function myTest() {
// using x inside this function will generate an error
echo “<p>Variable x inside function is: $x</p>”;
}
myTest();
echo “<p>Variable x outside function is: $x</p>”;
?>
A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function:
Example
Variable with local scope:
<?php
function myTest() {
$x = 5; // local scope
echo “<p>Variable x inside function is: $x</p>”;
}
myTest();
// using x outside the function will generate an error
echo “<p>Variable x outside function is: $x</p>”;
?>
You can have local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared.
PHP The global Keyword
The global keyword is used to access a global variable from within a function.
To do this, use the global keyword before the variables (inside the function):
Example
<?php
$x = 5;
$y = 10;
function myTest() {
global $x, $y;
$y = $x + $y;
}
myTest();
echo $y; // outputs 15
?>
PHP also stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable. This array is also accessible from within functions and can be used to update global variables directly.
The example above can be rewritten like this:
Example
<?php
$x = 5;
$y = 10;
function myTest() {
$GLOBALS[‘y’] = $GLOBALS[‘x’] + $GLOBALS[‘y’];
}
myTest();
echo $y; // outputs 15
?>
Then, each time the function is called, that variable will still have the information it contained from the last time the function was called.
Note: The variable is still local to the function.
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