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1.3 PHP Syntax

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 1: Hello World

<!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 2: PHP Case Sensitivity - Hello World

<!DOCTYPE html>
<html>
<body>

<?php
ECHO "Hello World!<br>";
echo "Hello World!<br>";
EcHo "Hello World!<br>";
?>

</body>
</html>

Note: However; all variable names are case-sensitive!
Look at the example below; only the first statement will display the value of the $color variable! This is because $color, $COLOR, and $coLOR are treated as three different variables:

Example 3: PHP Case Sensitivity - Color World

<!DOCTYPE html>
<html>
<body>

<?php
$color = "red";
echo "My car is " . $color . "<br>";
echo "My house is " . $COLOR . "<br>";
echo "My boat is " . $coLOR . "<br>";
?>

</body>
</html>

PHP Fundamentals course home
Module 1. Introduction to PHP

Navigate this module

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Example files created in this module:
My first PHP page - Hello World PHP Case Sensitivity - Hello World PHP Case Sensitivity - Color World Syntax for single-line comments Syntax for multiple-line comments: Using comments to leave out parts of the code: Declaring PHP Variables Output Variables part 1 Output Variables part 2 Output Variables part 3 Variable with global scope: Variable with local scope: PHP The global Keyword part 1 PHP The global Keyword part 2 PHP The static Keyword The PHP echo Statement part 1 The PHP echo Statement part 2 The PHP print Statement part 1 The PHP print Statement part 2