PHP: Basic Syntax

PHP code is signified to the PHP interpreter enclosed within special tags.

The standard and the most common is the open tag <?php ending with the delimiter ?> 

				
					<?php 
						echo 'Hello, World!';  
					?>

Statements in PHP end with a semicolon (;) and PHP files end with a .php extension.

HTML/Script Tag

As in the case of JavaScript, PHP code can also be enclosed between the <script> tags by setting the language attribute to php 

					
						<script language="php">
							echo 'Hello, World!'; 
						</script>

PHP Short Open Tag

PHP also has a provision for a shorter open tag <?. It can be enabled in the php.ini configuration file (usually located in the /etc/php5/apache2 directory) by setting short_open_tag to On, which otherwise was set to Off by default.

php.ini Configuration File

After saving the changes, restart the Apache server. The below script should print just Hello, World! 

					
						<? 
							echo 'Hello, World!'; 
						?>

The usage of short open tags however is not recommended.

ASP Style Tag

As in the case of short_open_tag described in the above section, ASP style tag can also be enabled by setting asp_tags to On in the php.ini configuration file. Restarting the Apache server thereafter, and running the below script should print Hello, World! 

					
						<%
							echo 'Hello, World!';  
						%>

Comments

Single-line comments in PHP can start either with a # (hash), shell-style, 

					
						<?php 	
							# this is a single-line comment
						?>

or with double-slashes, C++ style 

					
						<?php 	
							// this is also a single-line comment
						?>

Multiline comments in PHP are C-like 

					
						<?php 
							/* this is
							a multi-line
							comment */  
						?>

Case Sensitivity/Insensitivity

In PHP, the following are case insensitive:

  • built-in constructs (like echo and print)
  • keywords (like if, else,while, do, etc.)
  • user-defined function names
  • user-defined class names and class methods

The below script runs perfectly, despite using echo in all caps as ECHO 

					
						<script language="php">
							echo 'Hello, World!'; 
							ECHO 'Hello, World!';  
						</script>

However, constants, variables, array keys, class properties and class constants are all case sensitive.