The 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
?>
// PHP code goes here
?>
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>
<html>
<body>
<h1>My first PHP page</h1>
<?php
echo "Hello World!";
?>
</body>
</html>
Note: PHP statements are terminated by semicolon (;). The
closing tag of a block of PHP code also automatically implies a semicolon (so
you do not have to have a semicolon terminating the last line of a PHP block).
Comments are useful for:
In the example below, all three echo statements below are legal (and equal):
However; in PHP, all variables 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):
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 editing the code!Comments are useful for:
- To let others understand what you are doing - Comments let other programmers understand what you were doing in each step (if you work in a group)
- To remind yourself 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
Example
<!DOCTYPE html>
<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 more than
one line
*/
?>
</body>
</html>
<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 more than
one line
*/
?>
</body>
</html>
PHP Case Sensitivity
In PHP, all user-defined functions, classes, and keywords (e.g. if, else, while, echo, etc.) 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!<br>";
echo "Hello World!<br>";
EcHo "Hello World!<br>";
?>
</body>
</html>
<html>
<body>
<?php
ECHO "Hello World!<br>";
echo "Hello World!<br>";
EcHo "Hello World!<br>";
?>
</body>
</html>
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 . "<br>";
echo "My house is " . $COLOR . "<br>";
echo "My boat is " . $coLOR . "<br>";
?>
</body>
</html>
<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>
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