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:
<html> <body> <h1>My first PHP page</h1> <?php echo "Hello World!"; ?> </body> </html>
Comments in PHP
A comment in PHP code is a line that is not read/executed as part of the program. Its only purpose is to be read by someone who is looking at the code. Comments can be used to:
- Help others to understand your code.
- When you re-visit the code, comment will help you understand the flow. Comments can remind you of what you were thinking when you wrote the code
PHP supports several ways of commenting:
<html> <body> <?php // This is a single-line comment # This is also a single-line comment /* This is a multiple-lines comment block that spans over multiple lines */ ?> </body> </html>
PHP Case Sensitivity
1. In PHP, all 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 legal (and equal):
<html> <body> <?php echo "Hello World!<br>"; Echo "Hello World!<br>"; ECHO "Hello World!<br>"; ?> </body> </html>
2. However all variable names are case-sensitive.
In 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):
<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>