PHP Basics - Intrepreted Scripting Language

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Basics

PHP is an interpreted scripting language embedded in HTML pages and executed by the web server or on the command line. Apache, IIS, and other web servers can execute PHP if the proper options are selected during the installation. Installation of PHP is not covered in this book. To obtain an accurate and complete guide for this installation, access: http://www.php.net .

As in any other programming language, PHP consists of expressions connected by operators and handled by commands. Operators are more or less the same as in the other scripting languages. Operator tables have been taken from the PHP on-line manual in their original format and are listed on the next two pages.

ASSOCIATIVELY	OPERATORS
Non-associative	New
Right	[
Non-associative	++--
Non-associative	! ~ - (int) (float) (string) (array) (object) @
Left	* / %
Left	+-.
Left	<< >>
Non-associative	< <= > >=
Non-associative	== != === !==
Left	&
Left	^
Left	\|
Left	&&
Left	\|\|
Left	?:
Right	= += -= *= /= .= %= &= \|= ^= <<= >>=
Left	And
Left	Xor
Left	Or
Left	,

Table 1.1: Operator Precedence

EXAMPLE	NAME	RESULT
-$a	Negation	Opposite of $a.
$a + $b	Addition	Sum of $a and $b.
$a - $b	Subtraction	Difference of $a and $b.
$a * $b	Multiplication	Product of $a and $b.
$a / $b	Division	Quotient of $a and $b.
$a % $b	Modulus	Remainder of $a divided by $b.

Table 1.2: Arithmetic Operators

EXAMPLE	NAME	RESULT
$a == $b	Equal	TRUE if $a is equal to $b.
$a === $b	Identical	TRUE if $a is equal to $b, and they are of the same type. (introduced in PHP 4)
$a != $b	Not equal	TRUE if $a is not equal to $b.
$a <> $b	Not equal	TRUE if $a is not equal to $b.
$a !== $b	Not identical	TRUE if $a is not equal to $b, or they are not of the same type. (introduced in PHP 4)
$a < $b	Less than	TRUE if $a is strictly less than $b.
$a > $b	Greater than	TRUE if $a is strictly greater than $b.
$a <= $b	Less than or equal to	TRUE if $a is less than or equal to $b.
$a >= $b	Greater than or equal to	TRUE if $a is greater than or equal to $b.

Table 1.3: Comparison Operators

Example	Name	Result
$a and $b	And	TRUE if both $a and $b are TRUE.
$a or $b	Or	TRUE if either $a or $b is TRUE.
$a xor $b	Xor	TRUE if either $a or $b is TRUE, but not both.
! $a	Not	TRUE if $a is not TRUE.
$a && $b	And	TRUE if both $a and $b are TRUE.
$a \|\| $b	Or	TRUE if either $a or $b is TRUE.

Table 1.4: Logical Operators

There is only one operator that can be regarded as a string operator: "." (dot) represents concatenation as in the following example:

     $a="Using PHP ";
     $b="with Oracle";
     $c=$a.$b;

The value of the variable $c is "Using PHP with Oracle".

PHP variables can be numeric or textual scalars, arrays indexed by numbers, associative arrays (also known as "hashes") and objects. All variables are prefixed by the dollar sign "$". There is no distinction between arrays, hashes and scalars based on the prefix, such as in Perl in which those are marked by @,% and $ respectively.

As in Perl, alphanumeric characters and underscore (_) characters are allowed in the variable names. Variables are weakly typed, meaning that the type cannot be declared. It is perfectly acceptable to assign a string to the numeric variable, or vice versa.

Generally speaking, PHP distinguishes between lowercase letters and uppercase letters. However, there are exceptions which will be pointed out as they are encountered. Again, PHP is embedded into HTML and can be mixed with HTML tags. Web servers interpret everything between the <?php and ?> as a PHP routine and passes it to the PHP interpreter either embedded in the server itself or called as a CGI script.

The following contains a few examples of PHP variables:

     $a=5;
     $b="Hello World!";
     $c=array("a",5,3.14,"Hello World",NULL);
     $d=TRUE;

See code depot for complete scripts

This is an excerpt from the book Easy Oracle PHP. You can get it for more than 30% by buying it directly from the publisher and get instant HTML-DB scripts from the code depot: