Web Standards Programmer's Reference: HTML, CSS, JavaScript®, Perl, Python®, and PHP

29.3. PHP Fundamentals

PHP scripts are stored in plaintext format and follow a specific syntax. The following sections introduce you to PHP's scripting structure and syntax.

29.3.1. PHP Beginning and Ending Tags

All PHP code needs to be enclosed within beginning and ending tags. The PHP beginning tag is <?php and the ending tag is ?>. For example, examine the following basic PHP script:

<?php
  print "Hello world. \n";
?>

Notice how the first line contains the beginning tag and the last line contains the ending tag. Because of PHP's interpretation of white space (generally ignored), you could just as easily use the following:

<?php  echo "Hello world. \n";  ?>

You can turn PHP processing on and off within a script by closing and reopening the PHP tags. For example, if you wanted to embed some complex HTML within a script (or embed simple scripts within XHTML), you could do something like the following:

<?php
      [php code here]
?>
      [XHTML code here]
<?php
      [more php code here]
?>...

Likewise, you can use PHP only where absolutely necessary in a document:

[XHTML code here]
<?php  [minimal php code here]  ?>
[XHTML code here]

29.3.2. Command Termination Character and Blocks of Code

PHP uses the semicolon character as the end marker for commands. The language also recognizes braces as the delimiter for blocks of code. For example, consider the following if construct:

if (condition) {
  [lines to execute if condition is true]
} else {
  [lines to execute if condition is false]
}

The braces in the ...