PHP Writing

This chapter will give you an idea of very basic syntax of PHP and very important to make your PHP foundation strong.

Writing PHP

Before we talk about PHP's syntax, let us first define what syntax is referring to.

Syntax - The rules that must be followed to write properly structured code.

PHP's syntax and semantics are similar to most other programming languages (C, Java, Perl) with the addition that all PHP code is contained with a tag, of sorts. All PHP code must be contained within the following

How PHP code is parsed?

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.' When PHP parses a file, it looks for opening and closing tags, which tell PHP to start and stop interpreting the code between them. Parsing in this manner allows PHP to be embedded in all sorts of different documents, as everything outside of a pair of opening and closing tags is ignored by the PHP parser. 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>

While the tags seen in one and two are both always available, one is the most commonly used, and recommended, of the two.

Short tags are only available when they are enabled via the  short_open_tag php.ini configuration file directive, or if PHP was configured with the--enable-short-tags option.

ASP style tags (example four) are only available when they are enabled via the  asp_tags php.ini configuration file directive.

Note: Using short tags should be avoided when developing applications or libraries that are meant for redistribution, or deployment on PHP servers which are not under your control, because short tags may not be supported on the target server. For portable, redistributable code, be sure not to use short tags.

Note: In PHP 5.2 and earlier, the parser does not allow the <?php opening tag to be the only thing in a file. This is allowed as of PHP 5.3.

Embedding PHP and HTML

Most of the time you will see PHP embedded in HTML documents, as in this example.

<p>This is going to be ignored.</p>

<?php echo 'While this is going to be parsed.'; ?>

<p>This will also be ignored.</p>

You can also use more advanced structures:

Example #1 Advanced embedding

<?php

if ($expression)

{

?>

<strong>This is true.</strong>

<?php

}

 else

{

?>

<strong>This is false.</strong>

<?php

}

?>

This works as expected, because when PHP hits the ?> closing tags, it simply starts outputting whatever it finds (except for an immediately following newline) until it hits another opening tag. The example given here is contrived, of course, but for outputting large blocks of text, dropping out of PHP parsing mode is generally more efficient than sending all of the text through echo() or print().

Note: Also note that if you are embedding PHP within XML or XHTML you will need to use the <?php ?> tags to remain compliant with standards.

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>

<?

$capital = 67;

print("Variable capital is $capital<br>");

print("Variable CaPiTaL is $CaPiTaL<br>");

?>

</body>

</html>

This will produce following result:

Variable capital is 67

Variable CaPiTaL is

Statements are expressions terminated by semicolons:

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:

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 following result:

Hello PHP!!!!!

Hope now you have basic knowledge of PHP Syntax.

 

Questions

  • What are the ways to write PHP code? [2 Marks]
  • How casn you embed PHP and HTML? Explain with necesary examples. [5,7 Matks]

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