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:

< !DOCTYPE class="attributecolor" style="color:red"> html="tagcolor" style="color:mediumblue">>
< html class="tagcolor" style="color:mediumblue">>
< body class="tagcolor" style="color:mediumblue">>

< h1 class="tagcolor" style="color:mediumblue">>My first PHP page< /h1 class="tagcolor" 

style="color:mediumblue">>

< ?php
class="phpnumbercolor" style="color:red"> class="phpkeywordcolor" style="color:mediumblue">
echo class="phpstringcolor" style="color:brown">"Hello World!";
class="phptagcolor" style="color:red">?>

< /body class="tagcolor" style="color:mediumblue">>
< /html class="tagcolor" style="color:mediumblue">> 

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:

< !DOCTYPE class="attributecolor" style="color:red"> html="tagcolor" style="color:mediumblue">>
<  html class="tagcolor" style="color:mediumblue">>
< body class="tagcolor" style="color:mediumblue">>

< ?php
class="phpnumbercolor" style="color:red"> class="phpkeywordcolor" style="color:mediumblue">
ECHO class="phpstringcolor" style="color:brown">"Hello World!< br>";
class="phpkeywordcolor" style="color:mediumblue">echo class="phpstringcolor" style="color:brown">
"Hello World!< br>";
class="phpnumbercolor" style="color:red"> class="phpkeywordcolor" style="color:mediumblue">
EcHo class="phpstringcolor" style="color:brown">"Hello World!< br>";
class="phptagcolor" style="color:red">?>

< /body class="tagcolor" style="color:mediumblue">>
< /html class="tagcolor" style="color:mediumblue">> 

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:

 < !DOCTYPE class="attributecolor" style="color:red"> html="tagcolor" style="color:mediumblue">>
< html class="tagcolor" style="color:mediumblue">>
< body class="tagcolor" style="color:mediumblue">>

< ?php
$color = class="phpstringcolor" style="color:brown">"red";
class="phpnumbercolor" style="color:red"> class="phpkeywordcolor" style="color:mediumblue">
echo class="phpstringcolor" style="color:brown">"My car is " . $color . class="phpstringcolor" 

style="color:brown">"< br>";
class="phpkeywordcolor" style="color:mediumblue">
echo class="phpstringcolor" style="color:brown">"My house is " . $COLOR . class="phpstringcolor"  

style="color:brown">"< br>";
class="phpkeywordcolor" style="color:mediumblue">echo class="phpstringcolor" style="color:brown">
"My boat is " . $coLOR . class="phpstringcolor" style="color:brown">"< br>";
class="phptagcolor" style="color:red">?>

< /body class="tagcolor" style="color:mediumblue">>
< /html class="tagcolor" style="color:mediumblue">>