PHP 5 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:

<!DOCTYPE html>
<html>
<body>

<h1>My first PHP page</h1>

<?php
echo "Hello World!";
?>

</body>
</html>

 

Note: PHP statements end with a semicolon (;).

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:

  • Let others understand what you are doing
  • install PHP
  • Remind yourself of what you did - Most programmers have experienced coming back to their own work a year or two later and having to re-figure out what they did. Comments can remind you of what you were thinking when you wrote the code

PHP supports several ways of commenting:

Example:

<!DOCTYPE html>
  <html>
  <body>

  <h1>My first PHP page</h1>

  <?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
  */

  // You can also use comments to leave out parts of a code line
  $x = 5 /* + 15 */ + 5;
  echo $x;
  ?>

  </body>
  </html>

 

PHP Case Sensitivity

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):

Example:

<!DOCTYPE html>
<html>
<body>

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

  </body>
  </html>

 

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):

Example:

<!DOCTYPE html>
<html>
<body>

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

</body>
</html>