PHP Syntax
Overview
This chapter will give you an idea of very basic
syntax of PHP and very important to make your PHP foundation strong.
Escaping to PHP
The PHP parsing engine needs a way to differentiate
PHP code from other elements in the page. The mechanism for doing so is known
as 'escaping to PHP'. There are four ways to do this −
Canonical PHP tags
The most universally effective PHP tag style is
−
<?php...?>
If you use this style, you can be positive that
your tags will always be correctly interpreted.
Short-open (SGML-style) tags
Short or short-open tags look like this −
<?...?>
Short tags are, as one might expect, the shortest
option You must do one of two things to enable PHP to recognize the tags
−
·
Choose the --enable-short-tags
configuration option when you're building PHP.
·
Set the short_open_tag setting in your
php.ini file to on. This option must be disabled to parse XML with PHP because
the same syntax is used for XML tags.
ASP-style tags
ASP-style tags mimic the tags used by Active Server
Pages to delineate code blocks. ASP-style tags look like this −
<%...%>
To use ASP-style tags, you will need to set the
configuration option in your php.ini file.
HTML script tags
HTML script tags look like this −
<script language="PHP">...</script>
Commenting PHP
Code
A comment is the portion of a
program that exists only for the human reader and stripped out before
displaying the programs result. There are two commenting formats in PHP −
Single-line comments − They are generally used for short
explanations or notes relevant to the local code. Here are the examples of
single line comments.
<?
# This
is a comment, and
# This
is the second line of the comment
// This
is a comment too. Each style comments only
print "An example with single line
comments";
?>
Multi-lines printing − Here are the examples to print
multiple lines in a single print statement −
<?
# First
Example
print <<<END
This uses the "here document" syntax to output
multiple lines with $variable interpolation. Note
that the here document terminator must
appear on a
line with just a semicolon no extra
whitespace!
END;
#
Second Example
print "This spans
multiple lines. The newlines will be
output as well";
?>
Multi-lines comments − They are generally used to provide
pseudocode algorithms and more detailed explanations when necessary. The
multiline style of commenting is the same as in C. Here are the example of
multi lines comments.
<?
/* This
is a comment with multiline
Author : Mohammad Mohtashim
Purpose: Multiline Comments Demo
Subject: PHP
*/
print "An example with multi line
comments";
?>
PHP is
whitespace insensitive
Whitespace is the stuff you type that is typically
invisible on the screen, including spaces, tabs, and carriage returns
(end-of-line characters).
PHP whitespace insensitive means that it almost
never matters how many whitespace characters you have in a row.one whitespace
character is the same as many such characters.
For example, each of the following PHP statements
that assigns the sum of 2 + 2 to the variable $four is equivalent −
$four = 2 + 2; // single spaces
$four <tab>=<tab2<tab>+<tab>2 ; //
spaces and tabs
$four =
2+
2; //
multiple lines
PHP is case
sensitive
Yeah it is true that PHP is a case sensitive
language. Try out following example −
<html>
<body>
<?php
$capital = 67;
print("Variable capital is
$capital<br>");
print("Variable CaPiTaL is
$CaPiTaL<br>");
?>
</body>
</html>
This will produce the following result −
Variable
capital is 67
Variable
CaPiTaL is
Statements are
expressions terminated by semicolons
A statement in PHP is any
expression that is followed by a semicolon (;).Any sequence of valid PHP
statements that is enclosed by the PHP tags is a valid PHP program. Here is a
typical statement in PHP, which in this case assigns a string of characters to
a variable called $greeting −
$greeting
= "Welcome to PHP!";
Expressions are
combinations of tokens
The smallest building blocks of PHP are the
indivisible tokens, such as numbers (3.14159), strings (.two.), variables
($two), constants (TRUE), and the special words that make up the syntax of PHP
itself like if, else, while, for and so forth
Braces make
blocks
Although statements cannot be combined like
expressions, you can always put a sequence of statements anywhere a statement
can go by enclosing them in a set of curly braces.
Here both statements are equivalent −
if (3 == 2 + 1)
print("Good - I haven't totally lost
my mind.<br>");
if (3 == 2 + 1) {
print("Good - I haven't totally");
print("lost my mind.<br>");
}
Running PHP
Script from Command Prompt
Yes you can run your PHP script on your command
prompt. Assuming you have following content in test.php file
<?php
echo "Hello PHP!!!!!";
?>
Now run this script as command prompt as follows
−
$ php
test.php
It will produce the following result −
Hello
PHP!!!!!
Hope now you have basic knowledge of PHP Syntax.