PHP es un lenguaje de programación del lado del servidor creado en 1995 por Rasmus Lerdorf.

PHP es un lenguaje de secuencias de comandos de uso general de código abierto ampliamente utilizado que es especialmente adecuado para el desarrollo web y puede integrarse en HTML.

¿Para qué se usa PHP?

A partir de octubre de 2018, PHP se utiliza en el 80% de los sitios web cuyo idioma del lado del servidor es conocido. Normalmente se utiliza en sitios web para generar contenido de páginas web de forma dinámica. Los casos de uso incluyen:

• Sitios web y aplicaciones web (secuencias de comandos del lado del servidor)
• Secuencias de comandos de línea de comandos
• Aplicaciones de escritorio (GUI)

Normalmente, se utiliza en el primer formulario para generar contenido de páginas web de forma dinámica. Por ejemplo, si tiene un sitio web de blog, puede escribir algunos scripts PHP para recuperar las publicaciones de su blog de una base de datos y mostrarlas. Otros usos de los scripts PHP incluyen:

• Procesar y guardar la entrada del usuario de los datos del formulario
• Configurar y trabajar con cookies de sitios web
• Restringir el acceso a determinadas páginas de su sitio web

Facebook, la plataforma de redes sociales más grande, está escrita con PHP

¿Cómo funciona PHP?

Todo el código PHP se ejecuta solo en un servidor web, no en su computadora local. Por ejemplo, si completa un formulario en un sitio web y lo envía, o hace clic en un enlace a una página web escrita en PHP, no se ejecutará ningún código PHP real en su computadora. En cambio, los datos del formulario o la solicitud de la página web se envían a un servidor web para ser procesados ​​por los scripts PHP. Luego, el servidor web le envía el HTML procesado (que es de donde proviene el 'Preprocesador de hipertexto' en el nombre), y su navegador web muestra los resultados. Por esta razón, no puede ver el código PHP de un sitio web, solo el HTML resultante que han producido los scripts PHP.

Esto se ilustra a continuación:

PHP es un lenguaje interpretado. Esto significa que cuando realiza cambios en su código fuente, puede probar estos cambios inmediatamente, sin necesidad de compilar primero su código fuente en formato binario. Omitir el paso de compilación hace que el proceso de desarrollo sea mucho más rápido.

El código PHP se incluye entre and ?> tags and can then be embedded into HTML.

Installation

PHP can be installed with or without a web server.

GNU/Linux

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

sudo apt install php

On Centos 6 or 7 you can install by :

sudo yum install php

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

php file.php

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

sudo apt install apache2 libapache2-mod-php

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

PHP Frameworks

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

• You don't have to reinvent the wheel every time you create a project, a lot of the nuances are already taken care for you
• They are usually well-structured so that it helps in the separation of concerns
• Most frameworks tend the follow the best practices of the language
• A lot of them follow the MVC (Model-View-Controller) pattern so that it separates the presentation layer from logic

Popular frameworks

• CodeIgniter
• Laravel
• Symfony
• Zend
• CakePHP
• FuelPHP
• Slim
• Yii 2

Basic Syntax

PHP scripts can be placed anywhere in a document, and always start with and end 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:

Developer News

The output of that would be:

Developer News The Best PHP Examples

Comments

PHP supports several ways of commenting:

• Single-line comments:
• Multi-line comments:

Case Sensitivity

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

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

      
"; echo "Welcome to Developer News
"; EcHo "Enjoy all of the ad-free articles
"; ?>

Sin embargo, todos los nombres de variables distinguen entre mayúsculas y minúsculas. En el siguiente ejemplo, solo la primera declaración es válida y mostrará el valor de la $namevariable. $NAMEy $NaMeambos se tratan como variables diferentes:

    
"; echo "Hi! My name is " . $NAME . "
"; echo "Hi! My name is " . $NaMe . "
"; ?>

Variables

Las variables son la forma principal de almacenar información en un programa PHP.

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:

Rules for PHP variables

• Variable declarations starts with $, followed by the name of the variable
• Variable names can only start with an upper or lowercase letter or an underscore (_)
• Variable names can only contain letters, numbers, or underscores (A-z, 0-9, and _). Other special characters like + - % ( ) . & are invalid
• Variable names are case sensitive

Some examples of allowed variable names:

• $my_variable
• $anotherVariable
• $the2ndVariable

Predefined Variables

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.

• $this
• $_GET
• $_POST
• $_SERVER
• $_FILES

PHP Data Types

Variables can store data of different types such as:

• String ("Hello")
• Integer (5)
• Float (also called double) (1.0)
• Boolean ( 1 or 0 )
• Array ( array("I", "am", "an", "array") )
• Object
• NULL
• Resource

Strings

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

$x = "Hello!"; $y = 'Hello!';

Integers

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

Rules for integers:

• Integers must have at least one digit
• Integers must not have a decimal point
• Integers can be either positive or negative

$x = 5;

Floats

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

$x = 5.01;

Booleans

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

$x = true; $y = false;

Arrays

An array stores multiple values in one single variable.

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

NULL

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.

Classes and Objects

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.

model = "Tesla"; } } // create an object $Lightning = new Car(); // show object properties echo $Lightning->model; ?>

PHP Resource

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.

doc) . "\n";

Strings

A string is series of characters. These can be used to store any textual information in your application.

There are a number of different ways to create strings in PHP.

Single Quotes

Simple strings can be created using single quotes.

$name = 'Joe';

To include a single quote in the string, use a backslash to escape it.

$last_name = 'O\'Brian';

Double Quotes

You can also create strings using double quotes.

$name = "Joe";

To include a double quote, use a backslash to escape it.

$quote = "Mary said, \"I want some toast,\" and then ran away.";

Double quoted strings also allow escape sequences. These are special codes that put characters in your string that represent typically invisible characters. Examples include newlines \n, tabs \t, and actual backslashes \\.

You can also embed PHP variables in double quoted strings to have their values added to the string.

$name = 'Joe'; $greeting = "Hello $name"; // now contains the string "Hello Joe"

String Functions

Find the length of a string

The strlen() function returns the length of a string.

Find the number of words in a string

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

Reverse a String

The strrev() function reverses a string:

Search for text within a string

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

Replace Text Within a String

The str_replace() function replaces text in a string:

Constants

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).

Scope

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

? // Output: Learn to code and help nonprofits

Also, when you are creating classes, you can declare your own constants.

class Human { const TYPE_MALE = 'm'; const TYPE_FEMALE = 'f'; const TYPE_UNKNOWN = 'u'; // When user didn't select his gender ............. }

Note: If you want to use those constants inside the Human class, you can refer them as self::CONSTANT_NAME. If you want to use them outside the class, you need to refer them as Human::CONSTANT_NAME.

Operators

PHP contains all the normal operators one would expect to find in a programming language.

A single “=” is used as the assignment operator and a double “==” or triple “===” is used for comparison.

The usual “” can also be used for comparison and “+=” can be used to add a value and assign it at the same time.

Most notable is the use of the “.” to concatenate strings and “.=” to append one string to the end of another.

New to PHP 7.0.X is the Spaceship operator (). The spaceship operator returns -1, 0 or 1 when $a is less than, equal to, or greater than $b.

If / Else / Elseif Statements

If / Else is a conditional statement where depending on the truthiness of a condition, different actions will be performed.

Note: The {} brackets are only needed if the condition has more than one action statement; however, it is best practice to include them regardless.

If Statement

Note: You can nest as many statements in an "if" block as you'd like; you are not limited to the amount in the examples.

If/Else Statement

Note: The else statement is optional.

If/Elseif/Else Statement

Note:elseif should always be written as one word.

Nested If/Else Statement

Multiple Conditions

Multiple conditions can be used at once with the "or" (||), "xor", and "and" (&&) logical operators.

For instance:

Note: It's a good practice to wrap individual conditions in parens when you have more than one (it can improve readability).

Alternative If/Else Syntax

There is also an alternative syntax for control structures

 if (condition1): statement1; else: statement5; endif;

Ternary Operators

Ternary operators are basically single line if / else statements.

Suppose you need to display "Hello (user name)" if a user is logged in, and "Hello guest" if they're not logged in.

If / Else statement:

if($user == !NULL { $message = 'Hello '. $user; } else { $message = 'Hello guest'; }

Ternary operator:

$message = 'Hello '.($user == !NULL ? $user : 'Guest');

Switch

In PHP, the Switch statement is very similar to the JavaScript Switch statement (See the JavaScript Switch Guide to compare and contrast). It allows rapid case testing with a lot of different possible conditions, the code is also more readable.

Break

The break; statement exits the switch and goes on to run the rest of the application's code. If you do not use the break; statement you may end up running multiple cases and statements, sometimes this may be desired in which case you should not include the break; statement.

An example of this behavior can be seen below:

If $i = 1, the value of $j would be:

1

If $i = 2, the value of $j would be:

2

While break can be omitted without causing fall-through in some instances (see below), it is generally best practice to include it for legibility and safety (see below):

Example

Output

if case is 1 > Dice show number One. if case is 2 > Dice show number Two. if case is 3 > Dice show number Three or Four. if case is 4 > Dice show number Three or Four. if case is 5 > FiveSixDice show number Six. if case is 6 > SixDice show number Six. if none of the above > Dice show number unknown.

Loops

When you need to repeat a task multiple times, you can use a loop instead of adding the same code over and over again.

Using a break within the loop can stop the loop execution.

For loop

Loop through a block of code a specific number of times.

While loop

Loop through a block of code if a condition is true.

= 0) { echo "The index is ".$index.".\n"; $index--; } ?> /* Output: The index is 10. The index is 9. The index is 8. The index is 7. The index is 6. The index is 5. The index is 4. The index is 3. The index is 2. The index is 1. The index is 0. */

Do...While loop

Loop through a block of code once and continue to loop if the condition is true.

 0); ?> /* Output: Index: 3. Index: 2. Index: 1. */

Foreach loop

Loop through a block of code for each value within an array.

Functions

A function is a block of statements that can be used repeatedly in a program.

Simple Function + Call

function say_hello() { return "Hello!"; } echo say_hello();

Simple Function + Parameter + Call

function say_hello($friend) { return "Hello " . $friend . "!"; } echo say_hello('Tommy');

strtoupper - Makes all Chars BIGGER AND BIGGER!

function makeItBIG($a_lot_of_names) { foreach($a_lot_of_names as $the_simpsons) { $BIG[] = strtoupper($the_simpsons); } return $BIG; } $a_lot_of_names = ['Homer', 'Marge', 'Bart', 'Maggy', 'Lisa']; var_dump(makeItBIG($a_lot_of_names));

Arrays

Arrays are like regular variables, but hold multiple values in an ordered list. This can be useful if you have multiple values that are all related to each other, like a list of student names or a list of capital cities.

Types Of Arrays

In PHP, there are two types of arrays: Indexed arrays and Associative arrays. Each has their own use and we'll look at how to create these arrays.

Indexed Array

An indexed array is a list of ordered values. Each of these values in the array is assigned an index number. Indexes for arrays always start at 0 for the first value and then increase by one from there.

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

Associative Array

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.

 83, "Frank" => "93", "Benji" => "90"); ?>

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

Multidimensional Array

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.

 "Joe", "score" => 83, "last_name" => "Smith"), array("first_name" => "Frank", "score" => 92, "last_name" => "Barbson"), array("first_name" => "Benji", "score" => 90, "last_name" => "Warner") ); ?>

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

$students[0]['first_name']

Get The Length of an Array - The count() Function

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

Sorting Arrays

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

sort()

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

Output:

Array ( [0] => camp [1] => code [2] => free )

rsort()

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:

Array ( [0] => free [1] => code [2] => camp )

asort()

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

"free", "one"=>"code", "two"=>"camp"); asort($freecodecamp); print_r($freecodecamp); ?>

Output:

Array ( [two] => camp [one] => code [zero] => free )

ksort()

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

"free", "one"=>"code", "two"=>"camp"); ksort($freecodecamp); print_r($freecodecamp); ?>

Output:

Array ( [one] => code [two] => camp [zero] => free )

arsort()

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

"free", "one"=>"code", "two"=>"camp"); arsort($freecodecamp); print_r($freecodecamp); ?>

Output:

Array ( [zero] => free [one] => code [two] => camp )

krsort()

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

"free", "one"=>"code", "two"=>"camp"); krsort($freecodecamp); print_r($freecodecamp); ?>

Output:

Array ( [zero] => free [two] => camp [one] => code )

Forms

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.

Checking Required Inputs

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

Checking form to make sure its set

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

$firstName = $_GET['firstName'] if(isset($firstName)){ echo "firstName field is set". "
"; } else{ echo "The field is not set."."
"; }

Handling Form Input

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

$_POST["firstname"] or $_GET['lastname']