PHP ─ Syntax Overview

Escaping to PHP

The PHP parsing engine needs a way to differentiate PHP code from other elements on 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:

  1. Choose the –enable-short-tags configuration option when you’re building PHP.
  2. 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 is stripped out before displaying the result of the program. 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 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-line 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 assign 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 the following example:

<html>
<body>
<? $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 the following content in the test.php file

<?php echo  “Hello  PHP!!!!!”; ?>

Now run this script as a command prompt as follows:

$ php test.php

It will produce the following result

Hello  PHP!!!!!

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