PHP is a server-side scripting language created in 1995 by Rasmus Lerdorf.

PHP is a widely-used open source general-purpose scripting language that is especially suited for web development and can be embedded into HTML.

As of October 2018, PHP is used on 80% of websites whose server-side language is known. It is typically used on websites to generate web page content dynamically. Use-cases include:

Typically, it is used in the first form to generate web page content dynamically. For example, if you have a blog website, you might write some PHP scripts to retrieve your blog posts from a database and display them. Other uses for PHP scripts include:

The largest Social Networking Platform, Facebook is written using PHP

All PHP code is executed on a web server only, not on your local computer. For example, if you complete a form on a website and submit it, or click a link to a web page written in PHP, no actual PHP code runs on your computer. Instead, the form data or request for the web page gets sent to a web server to be processed by the PHP scripts. The web server then sends the processed HTML back to you (which is where 'Hypertext Preprocessor' in the name comes from), and your web browser displays the results. For this reason, you cannot see the PHP code of a website, only the resulting HTML that the PHP scripts have produced.

This is illustrated below:

PHP is an interpreted language. This means that when you make changes to your source code you can immediately test these changes, without first needing to compile your source code into binary form. Skipping the compilation step makes the development process much faster.

PHP code is enclosed between the tags and can then be embedded into HTML.

PHP can be installed with or without a web server.

On Debian based GNU/Linux distros, you can install by :

On Centos 6 or 7 you can install by :

After installing you can run any PHP files by simply doing this in terminal :

You can also install a localhost server to run PHP websites. For installing Apache Web Server :

Or you can also install PHP, MySQL & Web-server all by installing

XAMPP (free and open-source cross-platform web server solution stack package) or similar packages like WAMP

Since writing the whole code for a website is not really practical/feasible for most projects, most developers tend to use frameworks for the web development. The advantage of using a framework is that

PHP scripts can be placed anywhere in a document, and always start with . Also, PHP statements end with a semicolon (;).

Here's a simple script that uses the built-in echo function to output the text "The Best PHP Examples" to the page:

The output of that would be:

PHP supports several ways of commenting:

All keywords, classes, and functions are NOT case sensitive.

In the example below, all three echo statements are valid:

However, all variable names are case sensitive. In the example below, only the first statement is valid and will display the value of the $name variable. $NAME and $NaMe are both treated as different variables:

Variables are the main way to store information in a PHP program.

All variables in PHP start with a leading dollar sign like $variable_name. To assign a variable, use the = operator, with the name of the variable on the left and the expression to be evaluated on the right.

Syntax:

Some examples of allowed variable names:

PHP has several special keywords that, while they are "valid" variable names, cannot be used for your variables. The reason for this is that the language itself has already defined those variables and they have are used for special purposes. Several examples are listed below, for a complete list see the PHP documentation site.

Variables can store data of different types such as:

A string is a sequence of characters. It can be any text inside quotes (single or double):

An integer data type is a non-decimal number between -2,147,483,648 and 2,147,483,647.

Rules for integers:

$x = 5;

A float, or floating point number, is a number with a decimal point.

$x = 5.01;

A Boolean represents two possible states: TRUE or FALSE. Booleans are often used in conditional testing.

An array stores multiple values in one single variable.

$colors = array("Magenta", "Yellow", "Cyan");

Null is a special data type that can only have the value null. Variables can be declared with no value or emptied by setting the value to null. Also, if a variable is created without being assigned a value, it is automatically assigned null.

A class is a data structure useful for modeling things in the real world, and can contain properties and methods. Objects are instances a class, and are a convenient way to package values and functions specific to a class.

A resource is a special variable, holding a reference to an external resource. Resources are created and used by special functions. You can use getresourcetype() function to see resource type.

Find the number of words in a stringThe strwordcount() function returns the number of words in a string:

The strrev() function reverses a string:

The strpos() function searches for text in a string:

The str_replace() function replaces text in a string:

Constants are a type of variable in PHP. The define() function to set a constant takes three arguments - the key name, the key's value, and a Boolean (true or false) which determines whether the key's name is case-insensitive (false by default). A constant's value cannot be altered once it is set. It is used for values which rarely change (for example a database password OR API key).

It is important to know that unlike variables, constants ALWAYS have a global scope and can be accessed from any function in the script.

$shopping_list[0] would return "eggs", $shopping_list[1] would return "milk", and $shopping_list[2] would return "cheese".

An associative array is a list of values that are accessed via a key instead of index numbers. The key can be any value but it must be unique to the array.

$student_scores['Joe'] would return 83, $student_scores['Frank'] would return 93, $student_scores['Benji'] would return 90.

A multidimensional array is an array that contains other arrays. This lets you create complex data structures that can model a very complex group of data.

Now you can get the first student's first_name with:

The count() function is used to return the length (the number of elements) of an array:

PHP offers several functions to sort arrays. This page describes the different functions and includes examples.

The sort() function sorts the values of an array in ascending alphabetical/numerical order (E.g. A, B, C, D, E... 1, 2, 3, 4, 5...)

Output:

The rsort() functions sort the values of an array in descending alphabetical/numerical order (E.g. Z, Y, X, W, V... 5, 4, 3, 2, 1...)

Output:

The asort() function sorts an associative array, by its values, in ascending alphabetical/numerical order (E.g. A, B, C, D, E... 1, 2, 3, 4, 5...)

Output:

The ksort() function sorts an associative array, by its keys, in ascending alphabetical/numerical order (E.g. A, B, C, D, E... 1, 2, 3, 4, 5...)

Output:

The arsort() function sorts an associative array, by its values, in descending alphabetical/numerical order (E.g. Z, Y, X, W, V... 5, 4, 3, 2, 1...)

Output:

The krsort() function sorts an associative array, by its keys in descending alphabetical/numerical order (E.g. Z, Y, X, W, V... 5, 4, 3, 2, 1...)

Output:

Forms are a way for users to enter data or select data from the webpage. Forms can store data as well as allow the information to be retrieved for later use.

To make a form to work in languages like PHP you need some basic attributes in html. In most cases PHP uses 'post' and 'get' super global variables to get the data from form.

The 'method' attribute here tell the form the way to send the form data. Then the 'action' attribute tell where to send form data to process. Now the 'name' attribute is very important and it should be unique because in PHP the value of the name work as the identity of that input field.

PHP has a few functions to check if the required inputs have been met. Those functions are isset, empty, and is_numeric.

The isset checks to see if the field has been set and isn't null. Example:

One can get form inputs with global variables $POST and $GET.