Introduction to PHP

A PHP file may contain text, HTML tags and scripts. Scripts in a PHP file are executed on the server.

What You Should Already Know

Before you continue you should have a basic understanding of the following:

• HTML / XHTML
• Some scripting knowledge

If you want to study these subjects first, find the tutorials on our Home page.

What is PHP?

• PHP stands for PHP: Hypertext Preprocessor
• PHP is a server-side scripting language, like ASP
• PHP scripts are executed on the server
• PHP supports many databases (MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, Generic ODBC, etc.)
• PHP is an open source software (OSS)
• PHP is free to download and use

What is a PHP File?

• PHP files may contain text, HTML tags and scripts
• PHP files are returned to the browser as plain HTML 
• PHP files have a file extension of ".php", ".php3", or ".phtml"

What is MySQL?

• MySQL is a database server
• MySQL is ideal for both small and large applications
• MySQL supports standard SQL
• MySQL compiles on a number of platforms
• MySQL is free to download and use

PHP + MySQL

• PHP combined with MySQL are cross-platform (means that you can develop in Windows and serve on a Unix platform)

Why PHP?

• PHP runs on different platforms (Windows, Linux, Unix, etc.)
• PHP is compatible with almost all servers used today (Apache, IIS, etc.)
• PHP is FREE to download from the official PHP resource: www.php.net
• PHP is easy to learn and runs efficiently on the server side

Where to Start?

• Install an Apache server on a Windows or Linux machine
• Install PHP on a Windows or Linux machine
• Install MySQL on a Windows or Linux machine
  
  
  

PHP Installation

What do You Need?

This tutorial will not explain how to install PHP, MySQL, or Apache Server.

If your server supports PHP - you don't need to do anything! You do not need to compile anything or install any extra tools  - just create some .php files in your web directory - and the server will parse them for you. Most web hosts offer PHP support.

However, if your server does not support PHP, you must install PHP. Below is a link to a good tutorial from PHP.net on how to install PHP5:

http://www.php.net/manual/en/install.php

Download PHP

Download PHP for free here: http://www.php.net/downloads.php

Download MySQL Database

Download MySQL for free here: http://www.mysql.com/downloads/index.html

Download Apache Server

Download Apache for free here: http://httpd.apache.org/download.cgi

PHP Syntax

You cannot view the PHP source code by selecting "View source" in the browser - you will only see the output from the PHP file, which is plain HTML. This is because the scripts are executed on the server before the result is sent back to the browser.

Basic PHP Syntax

A PHP scripting block always starts with <?php and ends with ?>. A PHP scripting block can be placed anywhere in the document.

On servers with shorthand support enabled you can start a scripting block with .

However, for maximum compatibility, we recommend that you use the standard form (<?php) rather than the shorthand form.

<?php

?>

A PHP file normally contains HTML tags, just like an HTML file, and some PHP scripting code.

Below, we have an example of a simple PHP script which sends the text "Hello World" to the browser:

<?php

					
					
					echo "Hello World";

					
					
					?>

Each code line in PHP must end with a semicolon. The semicolon is a separator and is used to distinguish one set of instructions from another.

There are two basic statements to output text with PHP: echo and print. In the example above we have used the echo statement to output the text "Hello World".

Comments in PHP

In PHP, we use // to make a single-line comment or /* and */ to make a large comment block.

<?php

//This is a comment

/*

	
	
	This is

	
	
	a comment

	
	
	block

	
	
	*/

?>

PHP Variables

Variables are used for storing values, such as numbers, strings or function results, so that they can be used many times in a script.

Variables in PHP

Variables are used for storing a values, like text strings, numbers or arrays.

When a variable is set it can be used over and over again in your script

All variables in PHP start with a $ sign symbol.

The correct way of setting a variable in PHP:

$var_name = value;

New PHP programmers often forget the $ sign at the beginning of the variable. In that case it will not work.

Let's try creating a variable with a string, and a variable with a number:

<?php

					
					
					$txt = "Hello World!";

					
					
					$number = 16;

					
					
					?>

PHP is a Loosely Typed Language

In PHP a variable does not need to be declared before being set.

In the example above, you see that you do not have to tell PHP which data type the variable is.

PHP automatically converts the variable to the correct data type, depending on how they are set.

In a strongly typed programming language, you have to declare (define) the type and name of the variable before using it.

In PHP the variable is declared automatically when you use it.

Variable Naming Rules

• A variable name must start with a letter or an underscore "_"
• A variable name can only contain alpha-numeric characters and underscores (a-Z, 0-9, and _ )
• A variable name should not contain spaces. If a variable name is more than one word, it should be separated with underscore ($my_string), or with capitalization ($myString)

PHP String

A string variable is used to store and manipulate a piece of text.

Strings in PHP

String variables are used for values that contains character strings.

In this tutorial we are going to look at some of the most common functions and operators used to manipulate strings in PHP.

After we create a string we can manipulate it. A string can be used directly in a function or it can be stored in a variable.

Below, the PHP script assigns the string "Hello World" to a string variable called $txt:

<?php

					
					
					$txt="Hello World";

					
					
					echo $txt;

					
					
					?>

The output of the code above will be:

Hello World

Now, lets try to use some different functions and operators to manipulate our string.

The Concatenation Operator

There is only one string operator in PHP.

The concatenation operator (.)  is used to put two string values together.

To concatenate two variables together, use the dot (.) operator:

<?php

					
					
					$txt1="Hello World";

					
					
					$txt2="1234";

					
					
					echo $txt1 . " " . $txt2;

					
					
					?>

The output of the code above will be:

Hello World 1234

If we look at the code above you see that we used the concatenation operator two times. This is because we had to insert a third string.

Between the two string variables we added a string with a single character, an empty space, to separate the two variables.

Using the strlen() function

The strlen() function is used to find the length of a string.

Let's find the length of our string "Hello world!":

<?php

					
					
					echo strlen("Hello world!");

					
					
					?>

The output of the code above will be:

12

The length of a string is often used in loops or other functions, when it is important to know when the string ends. (i.e. in a loop, we would want to stop the loop after the last character in the string)

Using the strpos() function

The strpos() function is used to search for a string or character within a string.

If a match is found in the string, this function will return the position of the first match. If no match is found, it will return FALSE.

Let's see if we can find the string "world" in our string:

<?php

					
					
					echo strpos("Hello world!","world");

					
					
					

					
					
					?>

The output of the code above will be:

6

As you see the position of the string "world" in our string is position 6. The reason that it is 6, and not 7, is that the first position in the string is 0, and not 1.

Complete PHP String Reference

For a complete reference of all string functions, go to our complete PHP String Reference.

The reference contains a brief description and examples of use for each function!

PHP Operators

Operators are used to operate on values.

PHP Operators

This section lists the different operators used in PHP.

Arithmetic Operators

Assignment Operators

Comparison Operators

Logical Operators

PHP If...Else Statements

The if, elseif and else statements in PHP are used to perform different actions based on different conditions.

Conditional Statements

Very often when you write code, you want to perform different actions for different decisions.

You can use conditional statements in your code to do this.

• if...else statement - use this statement if you want to execute a set of code when a condition is true and another if the condition is not true
• elseif statement - is used with the if...else statement to execute a set of code if one of several condition are true

The If...Else Statement

If you want to execute some code if a condition is true and another code if a condition is false, use the if....else statement.

Syntax

if (condition)

					
					
					  code to be executed if condition is true;

					
					
					else

					
					
					  code to be executed if condition is false;

Example

The following example will output "Have a nice weekend!" if the current day is Friday, otherwise it will output "Have a nice day!":

<?php

					
					
					$d=date("D");

					
					
					if ($d=="Fri")

					
					
					  echo "Have a nice weekend!"; 

					
					
					else

					
					
					  echo "Have a nice day!"; 

					
					
					?>

If more than one line should be executed if a condition is true/false, the lines should be enclosed within curly braces:

<?php

					
					
					$d=date("D");

					
					
					if ($d=="Fri")

					
					
					  {

					
					
					  echo "Hello!

					
					"; 

					
					
					  echo "Have a nice weekend!";

					
					
					  echo "See you on Monday!";

					
					
					  }

					
					
					?>

The ElseIf Statement

If you want to execute some code if one of several conditions are true use the elseif statement

Syntax

if (condition)

					
					
					  code to be executed if condition is true;

					
					
					elseif (condition)

					
					
					  code to be executed if condition is true;

						
						
						else

					
					
					  code to be executed if condition is false;

Example

The following example will output "Have a nice weekend!" if the current day is Friday, and "Have a nice Sunday!" if the current day is Sunday. Otherwise it will output "Have a nice day!":

<?php

	
	
	$d=date("D");

	
	
	if ($d=="Fri")

	
	
	  echo "Have a nice weekend!"; 

	
	
	elseif ($d=="Sun")

	
	
	  echo "Have a nice Sunday!"; 

	
	
	else

	
	
	  echo "Have a nice day!"; 

	
	
	?>

PHP Switch Statement

The Switch statement in PHP is used to perform one of several different actions based on one of several different conditions.

The Switch Statement

If you want to select one of many blocks of code to be executed, use the Switch statement.

The switch statement is used to avoid long blocks of if..elseif..else code.

Syntax

switch (expression)

					
					
					{

					
					
					case label1:

					
					
					  code to be executed if expression = label1;

					
					
					  break;  

					
					
					case label2:

					
					
					  code to be executed if expression = label2;

					
					
					  break;

					
					
					default:

					
					
					  code to be executed

						
						
						  if expression is different 

						
						
						  from both label1 and label2;

					
					
					}

Example

This is how it works:

• A single expression (most often a variable) is evaluated once
• The value of the expression is compared with the values for each case in the structure
• If there is a match, the code associated with that case is executed
• After a code is executed, break is used to stop the code from running into the next case
• The default statement is used if none of the cases are true

<?php

	
	
	switch ($x)

	
	
	{

	
	
	case 1:

	
	
	  echo "Number 1";

	
	
	  break;

	
	
	case 2:

	
	
	  echo "Number 2";

	
	
	  break;

	
	
	case 3:

	
	
	  echo "Number 3";

	
	
	  break;

	
	
	default:

	
	
	  echo "No number between 1 and 3";

	
	
	}

	
	
	?>

PHP Arrays

An array can store one or more values in a single variable name.

What is an array?

When working with PHP, sooner or later, you might want to create many similar variables.

Instead of having many similar variables, you can store the data as elements in an array.

Each element in the array has its own ID so that it can be easily accessed.

There are three different kind of arrays:

• Numeric array - An array with a numeric ID key
• Associative array - An array where each ID key is associated with a value
• Multidimensional array - An array containing one or more arrays

Numeric Arrays

A numeric array stores each element with a numeric ID key.

There are different ways to create a numeric array.

Example 1

In this example the ID key is automatically assigned:

$names = array("Peter","Quagmire","Joe");

Example 2

In this example we assign the ID key manually:

$names[0] = "Peter";

					
					
					$names[1] = "Quagmire";

					
					
					$names[2] = "Joe";

The ID keys can be used in a script:

<?php

$names[0] = "Peter";

					
					
					$names[1] = "Quagmire";

					
					
					$names[2] = "Joe";

echo $names[1] . " and " . $names[2] . 

					
					
					" are ". $names[0] . "'s neighbors";

					
					
					?>

The code above will output:

Quagmire and Joe are Peter's neighbors

Associative Arrays

An associative array, each ID key is associated with a value.

When storing data about specific named values, a numerical array is not always the best way to do it.

With associative arrays we can use the values as keys and assign values to them.

Example 1

In this example we use an array to assign ages to the different persons:

$ages = array("Peter"=>32, "Quagmire"=>30, "Joe"=>34);

Example 2

This example is the same as example 1, but shows a different way of creating the array:

$ages['Peter'] = "32";

					
					
					$ages['Quagmire'] = "30";

					
					
					$ages['Joe'] = "34";

The ID keys can be used in a script:

<?php

$ages['Peter'] = "32";

					
					
					$ages['Quagmire'] = "30";

					
					
					$ages['Joe'] = "34";

echo "Peter is " . $ages['Peter'] . " years old.";

					
					
					?>

The code above will output:

Peter is 32 years old.

Multidimensional Arrays

In a multidimensional array, each element in the main array can also be an array. And each element in the sub-array can be an array, and so on.

Example

In this example we create a multidimensional array, with automatically assigned ID keys:

$families = array

					
					
					(

					
					
					  "Griffin"=>array

					
					
					  (

					
					
					  "Peter",

					
					
					  "Lois",

					
					
					  "Megan"

					
					
					  ),

					
					
					  "Quagmire"=>array

					
					
					  (

					
					
					  "Glenn"

					
					
					  ),

					
					
					  "Brown"=>array

					
					
					  (

					
					
					  "Cleveland",

					
					
					  "Loretta",

					
					
					  "Junior"

					
					
					  )

					
					
					);

The array above would look like this if written to the output:

Array

					
					
					(

					
					
					[Griffin] => Array

					
					
					  (

					
					
					  [0] => Peter

					
					
					  [1] => Lois

					
					
					  [2] => Megan

					
					
					  )

					
					
					[Quagmire] => Array

					
					
					  (

					
					
					  [0] => Glenn

					
					
					  )

					
					
					[Brown] => Array

					
					
					  (

					
					
					  [0] => Cleveland

					
					
					  [1] => Loretta

					
					
					  [2] => Junior

					
					
					  )

					
					
					) 

Example 2

Lets try displaying a single value from the array above:

echo "Is " . $families['Griffin'][2] . 

					
					
					" a part of the Griffin family?";

The code above will output:

Is Megan a part of the Griffin family?

PHP Looping

Looping statements in PHP are used to execute the same block of code a specified number of times.

Looping

Very often when you write code, you want the same block of code to run a number of times. You can use looping statements in your code to perform this.

In PHP we have the following looping statements:

• while - loops through a block of code if and as long as a specified condition is true
• do...while - loops through a block of code once, and then repeats the loop as long as a special condition is true
• for - loops through a block of code a specified number of times
• foreach - loops through a block of code for each element in an array

The while Statement

The while statement will execute a block of code if and as long as a condition is true.

Syntax

while (condition)

					
					
					code to be executed;

Example

The following example demonstrates a loop that will continue to run as long as the variable i is less than, or equal to 5. i will increase by 1 each time the loop runs:

<?php 

					
					
					$i=1;

					
					
					while($i<=5)

					
					
					  {

					
					
					  echo "The number is " . $i . "

					
					";

					
					
					  $i++;

					
					
					  }

					
					
					?>

The do...while Statement

The do...while statement will execute a block of code at least once - it then will repeat the loop as long as a condition is true.

Syntax

do

					
					
					{

					
					
					code to be executed;

						
						
						}

					
					
					while (condition);

Example

The following example will increment the value of i at least once, and it will continue incrementing the variable i as long as it has a value of less than 5:

<?php 

					
					
					$i=0;

					
					
					do

					
					
					  {

					
					
					  $i++;

					
					
					  echo "The number is " . $i . "

					
					";

					
					
					  }

					
					
					while ($i<5);

					
					
					?>

The for Statement

The for statement is used when you know how many times you want to execute a statement or a list of statements.

Syntax

for (initialization; condition; increment)

					
					
					{

					
					
					  code to be executed;

					
					
					}

Note: The for statement has three parameters. The first parameter initializes variables, the second parameter holds the condition, and the third parameter contains the increments required to implement the loop. If more than one variable is included in the initialization or the increment parameter, they should be separated by commas. The condition must evaluate to true or false.

Example

The following example prints the text "Hello World!" five times:

<?php

					
					
					for ($i=1; $i<=5; $i++)

					
					
					{

					
					
					  echo "Hello World!

					
					";

					
					
					}

					
					
					?>

The foreach Statement

The foreach statement is used to loop through arrays.

For every loop, the value of the current array element is assigned to $value (and the array pointer is moved by one) - so on the next loop, you'll be looking at the next element.

Syntax

foreach (array as value)

					
					
					{

					
					
					    code to be executed;

					
					
					}

Example

The following example demonstrates a loop that will print the values of the given array:

<?php

					
					
					$arr=array("one", "two", "three");

foreach ($arr as $value)

					
					
					{

					
					
					  echo "Value: " . $value . "

					
					";

					
					
					}

					
					
					?>

PHP Functions

The real power of PHP comes from its functions.

In PHP - there are more than 700 built-in functions available.

PHP Functions

In this tutorial we will show you how to create your own functions.

For a reference and examples of the built-in functions, please visit our PHP Reference.

Create a PHP Function

A function is a block of code that can be executed whenever we need it.

Creating PHP functions:

• All functions start with the word "function()"
• Name the function - It should be possible to understand what the function does by its name. The name can start with a letter or underscore (not a number)
• Add a "{"  - The function code starts after the opening curly brace
• Insert the function code
• Add a "}"  - The function is finished by a closing curly brace

Example

A simple function that writes my name when it is called:

<?php

					
					
					function writeMyName()

					
					
					  {

					
					
					  echo "Kai Jim Refsnes";

					
					
					  }

writeMyName();

					
					
					?>

Use a PHP Function

Now we will use the function in a PHP script:

<?php

					
					
					function writeMyName()

					
					
					  {

					
					
					  echo "Kai Jim Refsnes";

					
					
					  }

echo "Hello world!

					
					";

					
					
					echo "My name is ";

					
					
					writeMyName();

					
					
					echo ".

					
					That's right, ";

					
					
					writeMyName();

					
					
					echo " is my name.";

					
					
					?>

The output of the code above will be:

Hello world!

					
					
					My name is Kai Jim Refsnes.

					
					
					That's right, Kai Jim Refsnes is my name.

PHP Functions - Adding parameters

Our first function (writeMyName()) is a very simple function. It only writes a static string.

To add more functionality to a function, we can add parameters. A parameter is just like a variable.

You may have noticed the parentheses after the function name, like: writeMyName(). The parameters are specified inside the parentheses.

Example 1

The following example will write different first names, but the same last name:

<?php

					
					
					function writeMyName($fname)

					
					
					  {

					
					
					  echo $fname . " Refsnes.

					
					";

					
					
					  }

echo "My name is ";

					
					
					writeMyName("Kai Jim");

echo "My name is ";

					
					
					writeMyName("Hege");

echo "My name is ";

					
					
					writeMyName("Stale");

					
					
					?>

The output of the code above will be:

My name is Kai Jim Refsnes.

					
					
					My name is Hege Refsnes.

					
					
					My name is Stale Refsnes.

Example 2

The following function has two parameters:

<?php

					
					
					function writeMyName($fname,$punctuation)

					
					
					  {

					
					
					  echo $fname . " Refsnes" . $punctuation . "

					
					";

					
					
					  }

echo "My name is ";

					
					
					writeMyName("Kai Jim",".");

echo "My name is ";

					
					
					writeMyName("Hege","!");

echo "My name is ";

					
					
					writeMyName("Ståle","...");

					
					
					?>

The output of the code above will be:

My name is Kai Jim Refsnes.

					
					
					My name is Hege Refsnes!

					
					
					My name is Ståle Refsnes...

PHP Functions - Return values

Functions can also be used to return values.

Example

<?php

					
					
					function add($x,$y)

					
					
					  {

					
					
					  $total = $x + $y;

					
					
					  return $total;

					
					
					  }

echo "1 + 16 = " . add(1,16);

					
					
					?>

The output of the code above will be:

1 + 16 = 17

PHP Forms and User Input

The PHP $_GET and $_POST variables are used to retrieve information from forms, like user input.

PHP Form Handling

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.

Form example:

					
					


						
						
					Name: 
						
						

						
						
					Age: 
						
						

						
						
					
						
						

						
						
					
					
					

The example HTML page above contains two input fields and a submit button. When the user fills in this form and click on the submit button, the form data is sent to the "welcome.php" file.

The "welcome.php" file looks like this:

Welcome .

					
					

					
					
					You are  years old.

A sample output of the above script may be:

Welcome John.

					
					
					You are 28 years old.

The PHP $_GET and $_POST variables will be explained in the next chapters.

Form Validation

User input should be validated whenever possible. Client side validation is faster, and will reduce server load.

However, any site that gets enough traffic to worry about server resources, may also need to worry about site security. You should always use server side validation if the form accesses a database.

A good way to validate a form on the server is to post the form to itself, instead of jumping to a different page. The user will then get the error messages on the same page as the form. This makes it easier to discover the error.

PHP $_GET

The $_GET variable is used to collect values from a form with method="get".

The $_GET Variable

The $_GET variable is an array of variable names and values sent by the HTTP GET method.

The $_GET variable is used to collect values from a form with method="get". Information sent from a form with the GET method is visible to everyone (it will be displayed in the browser's address bar) and it has limits on the amount of information to send (max. 100 characters).

Example

					
					


						
						
					Name: 
						
						

						
						
					Age: 
						
						

						
						
					
						
						

						
						
					
					
					

When the user clicks the "Submit" button, the URL sent could look something like this:

http://www.w3schools.com/welcome.php?name=Peter&age=37

The "welcome.php" file can now use the $_GET variable to catch the form data (notice that the names of the form fields will automatically be the ID keys in the $_GET array):

Welcome .

					
					

					
					
					You are  years old!

Why use $_GET?

Note: When using the $_GET variable all variable names and values are displayed in the URL. So this method should not be used when sending passwords or other sensitive information! However, because the variables are displayed in the URL, it is possible to bookmark the page. This can be useful in some cases.

Note: The HTTP GET method is not suitable on large variable values; the value cannot exceed 100 characters.

The $_REQUEST Variable

The PHP $_REQUEST variable contains the contents of both $_GET, $_POST, and $_COOKIE.

The PHP $_REQUEST variable can be used to get the result from form data sent with both the GET and POST methods.

Example

Welcome .

	
	

	
	
	You are  years old!

PHP $_POST

The $_POST variable is used to collect values from a form with method="post".

The $_POST Variable

The $_POST variable is an array of variable names and values sent by the HTTP POST method.

The $_POST variable is used to collect values from a form with method="post". Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.

Example

					
					


						
						
					Enter your name: 
						
						

						
						
					Enter your age: 
						
						

						
						
					
						
						

						
						
					
					
					

When the user clicks the "Submit" button, the URL will not contain any form data, and will look something like this:

http://www.w3schools.com/welcome.php

The "welcome.php" file can now use the $_POST variable to catch the form data (notice that the names of the form fields will automatically be the ID keys in the $_POST array):

Welcome .

					
					

					
					
					You are  years old!

Why use $_POST?

• Variables sent with HTTP POST are not shown in the URL
• Variables have no length limit

However, because the variables are not displayed in the URL, it is not possible to bookmark the page.

The $_REQUEST Variable

The PHP $_REQUEST variable contains the contents of both $_GET, $_POST, and $_COOKIE.

The PHP $_REQUEST variable can be used to get the result from form data sent with both the GET and POST methods.

Example

Welcome .

	
	

	
	
	

	
	
	

	
	
	You are  years old!