PHP - Introduction
PHP started out as a small open source project that evolved as more and more people found out how useful it was. Rasmus Lerdorf unleashed the first version of PHP way back in 1994.
PHP is a recursive acronym for "PHP: Hypertext Preprocessor".
PHP is a server side scripting language that is embedded in HTML. It is used to manage dynamic content, databases, session tracking, even build entire e-commerce sites.
It is integrated with a number of popular databases, including MySQL, PostgreSQL, Oracle, Sybase, Informix, and Microsoft SQL Server.
PHP is pleasingly zippy in its execution, especially when compiled as an Apache module on the Unix side. The MySQL server, once started, executes even very complex queries with huge result sets in record-setting time.
PHP supports a large number of major protocols such as POP3, IMAP, and LDAP. PHP4 added support for Java and distributed object architectures (COM and CORBA), making n-tier development a possibility for the first time.
PHP is forgiving: PHP language tries to be as forgiving as possible.
PHP Syntax is C-Like.
Common uses of PHP
PHP performs system functions, i.e. from files on a system it can create, open, read, write, and close them.
PHP can handle forms, i.e. gather data from files, save data to a file, through email you can send data, return data to the user.
You add, delete, modify elements within your database through PHP.
Access cookies variables and set cookies.
Using PHP, you can restrict users to access some pages of your website.
It can encrypt data.
Characteristics of PHP
Five important characteristics make PHP's practical nature possible −
- Simplicity
- Efficiency
- Security
- Flexibility
- Familiarity
"Hello World" Script in PHP
To get a feel for PHP, first start with simple PHP scripts. Since "Hello, World!" is an essential example, first we will create a friendly little "Hello, World!" script.
As mentioned earlier, PHP is embedded in HTML. That means that in amongst your normal HTML (or XHTML if you're cutting-edge) you'll have PHP statements like this −
<html> <head> <title>Hello World</title> </head> <body> <?php echo "Hello, World!";?> </body> </html>
It will produce following result −
Hello, World!
If you examine the HTML output of the above example, you'll notice that the PHP code is not present in the file sent from the server to your Web browser. All of the PHP present in the Web page is processed and stripped from the page; the only thing returned to the client from the Web server is pure HTML output.
All PHP code must be included inside one of the three special markup tags ATE are recognised by the PHP Parser.
<?php PHP code goes here ?> <? PHP code goes here ?> <script language = "php"> PHP code goes here </script>
A most common tag is the <?php...?> and we will also use the same tag in our tutorial.
From the next chapter we will start with PHP Environment Setup on your machine and then we will dig out almost all concepts related to PHP to make you comfortable with the PHP language.
PHP - Environment Setup
In order to develop and run PHP Web pages three vital components need to be installed on your computer system.
Web Server − PHP will work with virtually all Web Server software, including Microsoft's Internet Information Server (IIS) but then most often used is freely available Apache Server. Download Apache for free here − https://httpd.apache.org/download.cgi
Database − PHP will work with virtually all database software, including Oracle and Sybase but most commonly used is freely available MySQL database. Download MySQL for free here − https://www.mysql.com/downloads/
PHP Parser − In order to process PHP script instructions a parser must be installed to generate HTML output that can be sent to the Web Browser. This tutorial will guide you how to install PHP parser on your computer.
PHP Parser Installation
Before you proceed it is important to make sure that you have proper environment setup on your machine to develop your web programs using PHP.
Type the following address into your browser's address box.
http://127.0.0.1/info.php
If this displays a page showing your PHP installation related information then it means you have PHP and Webserver installed properly. Otherwise you have to follow given procedure to install PHP on your computer.
This section will guide you to install and configure PHP over the following four platforms −
Apache Configuration
If you are using Apache as a Web Server then this section will guide you to edit Apache Configuration Files.
Just Check it here − PHP Configuration in Apache Server
PHP.INI File Configuration
The PHP configuration file, php.ini, is the final and most immediate way to affect PHP's functionality.
Just Check it here − PHP.INI File Configuration
Windows IIS Configuration
To configure IIS on your Windows machine you can refer your IIS Reference Manual shipped along with IIS.
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.
PHP - Variable Types
The main way to store information in the middle of a PHP program is by using a variable.
Here are the most important things to know about variables in PHP.
All variables in PHP are denoted with a leading dollar sign ($).
The value of a variable is the value of its most recent assignment.
Variables are assigned with the = operator, with the variable on the left-hand side and the expression to be evaluated on the right.
Variables can, but do not need, to be declared before assignment.
Variables in PHP do not have intrinsic types - a variable does not know in advance whether it will be used to store a number or a string of characters.
Variables used before they are assigned have default values.
PHP does a good job of automatically converting types from one to another when necessary.
PHP variables are Perl-like.
PHP has a total of eight data types which we use to construct our variables −
Integers − are whole numbers, without a decimal point, like 4195.
Doubles − are floating-point numbers, like 3.14159 or 49.1.
Booleans − have only two possible values either true or false.
NULL − is a special type that only has one value: NULL.
Strings − are sequences of characters, like 'PHP supports string operations.'
Arrays − are named and indexed collections of other values.
Objects − are instances of programmer-defined classes, which can package up both other kinds of values and functions that are specific to the class.
Resources − are special variables that hold references to resources external to PHP (such as database connections).
The first five are simple types, and the next two (arrays and objects) are compound - the compound types can package up other arbitrary values of arbitrary type, whereas the simple types cannot.
We will explain only simple data type in this chapters. Array and Objects will be explained separately.
Integers
They are whole numbers, without a decimal point, like 4195. They are the simplest type .they correspond to simple whole numbers, both positive and negative. Integers can be assigned to variables, or they can be used in expressions, like so −
$int_var = 12345; $another_int = -12345 + 12345;
Integer can be in decimal (base 10), octal (base 8), and hexadecimal (base 16) format. Decimal format is the default, octal integers are specified with a leading 0, and hexadecimals have a leading 0x.
For most common platforms, the largest integer is (2**31 . 1) (or 2,147,483,647), and the smallest (most negative) integer is . (2**31 . 1) (or .2,147,483,647).
Doubles
They like 3.14159 or 49.1. By default, doubles print with the minimum number of decimal places needed. For example, the code −
<?php $many = 2.2888800; $many_2 = 2.2111200; $few = $many + $many_2; print("$many + $many_2 = $few <br>"); ?>
It produces the following browser output −
2.28888 + 2.21112 = 4.5
Boolean
They have only two possible values either true or false. PHP provides a couple of constants especially for use as Booleans: TRUE and FALSE, which can be used like so −
if (TRUE) print("This will always print<br>"); else print("This will never print<br>");
Interpreting other types as Booleans
Here are the rules for determine the "truth" of any value not already of the Boolean type −
If the value is a number, it is false if exactly equal to zero and true otherwise.
If the value is a string, it is false if the string is empty (has zero characters) or is the string "0", and is true otherwise.
Values of type NULL are always false.
If the value is an array, it is false if it contains no other values, and it is true otherwise. For an object, containing a value means having a member variable that has been assigned a value.
Valid resources are true (although some functions that return resources when they are successful will return FALSE when unsuccessful).
Don't use double as Booleans.
Each of the following variables has the truth value embedded in its name when it is used in a Boolean context.
$true_num = 3 + 0.14159; $true_str = "Tried and true" $true_array[49] = "An array element"; $false_array = array(); $false_null = NULL; $false_num = 999 - 999; $false_str = "";
NULL
NULL is a special type that only has one value: NULL. To give a variable the NULL value, simply assign it like this −
$my_var = NULL;
The special constant NULL is capitalized by convention, but actually it is case insensitive; you could just as well have typed −
$my_var = null;
A variable that has been assigned NULL has the following properties −
It evaluates to FALSE in a Boolean context.
It returns FALSE when tested with IsSet() function.
Strings
They are sequences of characters, like "PHP supports string operations". Following are valid examples of string
$string_1 = "This is a string in double quotes"; $string_2 = 'This is a somewhat longer, singly quoted string'; $string_39 = "This string has thirty-nine characters"; $string_0 = ""; // a string with zero characters
Singly quoted strings are treated almost literally, whereas doubly quoted strings replace variables with their values as well as specially interpreting certain character sequences.
<?php $variable = "name"; $literally = 'My $variable will not print!'; print($literally); print "<br>"; $literally = "My $variable will print!"; print($literally); ?>
This will produce following result −
My $variable will not print! My name will print
There are no artificial limits on string length - within the bounds of available memory, you ought to be able to make arbitrarily long strings.
Strings that are delimited by double quotes (as in "this") are preprocessed in both the following two ways by PHP −
Certain character sequences beginning with backslash (\) are replaced with special characters
Variable names (starting with $) are replaced with string representations of their values.
The escape-sequence replacements are −
- \n is replaced by the newline character
- \r is replaced by the carriage-return character
- \t is replaced by the tab character
- \$ is replaced by the dollar sign itself ($)
- \" is replaced by a single double-quote (")
- \\ is replaced by a single backslash (\)
Here Document
You can assign multiple lines to a single string variable using here document −
<?php $channel =<<<_XML_ <channel> <title>What's For Dinner</title> <link>http://menu.example.com/ </link> <description>Choose what to eat tonight.</description> </channel> _XML_; echo <<<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; print $channel; ?>
This will produce following result −
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! <channel> <title>What's For Dinner<title> <link>http://menu.example.com/<link> <description>Choose what to eat tonight.</description>
Variable Scope
Scope can be defined as the range of availability a variable has to the program in which it is declared. PHP variables can be one of four scope types −
Variable Naming
Rules for naming a variable is −
Variable names must begin with a letter or underscore character.
A variable name can consist of numbers, letters, underscores but you cannot use characters like + , - , % , ( , ) . & , etc
There is no size limit for variables.
PHP - Constants Types
A constant is a name or an identifier for a simple value. A constant value cannot change during the execution of the script. By default, a constant is case-sensitive. By convention, constant identifiers are always uppercase. A constant name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. If you have defined a constant, it can never be changed or undefined.
To define a constant you have to use define() function and to retrieve the value of a constant, you have to simply specifying its name. Unlike with variables, you do not need to have a constant with a $. You can also use the function constant() to read a constant's value if you wish to obtain the constant's name dynamically.
constant() function
As indicated by the name, this function will return the value of the constant.
This is useful when you want to retrieve value of a constant, but you do not know its name, i.e. It is stored in a variable or returned by a function.
constant() example
<?php define("MINSIZE", 50); echo MINSIZE; echo constant("MINSIZE"); // same thing as the previous line ?>
Only scalar data (boolean, integer, float and string) can be contained in constants.
Differences between constants and variables are
There is no need to write a dollar sign ($) before a constant, where as in Variable one has to write a dollar sign.
Constants cannot be defined by simple assignment, they may only be defined using the define() function.
Constants may be defined and accessed anywhere without regard to variable scoping rules.
Once the Constants have been set, may not be redefined or undefined.
Valid and invalid constant names
// Valid constant names
define("ONE", "first thing");
define("TWO2", "second thing");
define("THREE_3", "third thing");
define("__THREE__", "third value");
// Invalid constant names
define("2TWO", "second thing");
PHP Magic constants
PHP provides a large number of predefined constants to any script which it runs.
There are five magical constants that change depending on where they are used. For example, the value of __LINE__ depends on the line that it's used on in your script. These special constants are case-insensitive and are as follows −
A few "magical" PHP constants are given below −
| Sr.No | Name & Description | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| 1 | __LINE__ The current line number of the file. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2 | __FILE__ The full path and filename of the file. If used inside an include, the name of the included file is returned. Since PHP 4.0.2, __FILE__ always contains an absolute path whereas in older versions it contained relative path under some circumstances. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 3 | __FUNCTION__ The function name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the function name as it was declared (case-sensitive). In PHP 4 its value is always lowercased. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 4 | __CLASS__ The class name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the class name as it was declared (case-sensitive). In PHP 4 its value is always lowercased. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 5 | __METHOD__ The class method name. (Added in PHP 5.0.0) The method name is returned as it was declared (case-sensitive). PHP - Operator Types What is Operator? Simple answer can be given using expression 4 + 5 is equal to 9. Here 4 and 5 are called operands and + is called operator. PHP language supports following type of operators.
Lets have a look on all operators one by one. Arithmetic OperatorsThere are following arithmetic operators supported by PHP language − Assume variable A holds 10 and variable B holds 20 then −
Comparison OperatorsThere are following comparison operators supported by PHP language Assume variable A holds 10 and variable B holds 20 then −
Logical OperatorsThere are following logical operators supported by PHP language Assume variable A holds 10 and variable B holds 20 then −
Assignment OperatorsThere are following assignment operators supported by PHP language −
Conditional OperatorThere is one more operator called conditional operator. This first evaluates an expression for a true or false value and then execute one of the two given statements depending upon the result of the evaluation . The conditional operator has this syntax −
Operators CategoriesAll the operators we have discussed above can be categorised into following categories −
Precedence of PHP OperatorsOperator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator − For example x = 7 + 3 * 2; Here x is assigned 13, not 20 because operator * has higher precedence than + so it first get multiplied with 3*2 and then adds into 7. Here operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.
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