COMP284 Scripting Languages – Handouts
COMP284 Scripting Languages
Lecture 9: PHP (Part 1)
Handouts
Ullrich Hustadt
Department of Computer Science
School of Electrical Engineering, Electronics, and Computer Science
University of Liverpool
Contents
1 PHP
Motivation
2 Overview
Features
Applications
3 Types and Variables
Types
Variables
Type juggling and Type casting
Comparisons
COMP284 Scripting Languages Lecture 9 Slide L9 – 1
PHP Motivation
Common Gateway Interface — CGI
The Common Gateway Interface (CGI) is a standard method for web
servers to use external applications, a CGI program, to dynamically
generate web pages
1 A web client generates a client request, for example, from a HTML
form, and sends it to a web server
2 The web server selects a CGI program to handle the request,
converts the client request to a CGI request, executes the program
3 The CGI program then processes the CGI request and the server passes
the program’s response back to the client
COMP284 Scripting Languages Lecture 9 Slide L9 – 2
PHP Motivation
Disadvantages of CGI/Perl
• A distinction is made between static web pages and
dynamic web pages created by an external program
• Using Perl scripting it is difficult to add ‘a little bit’ of
dynamic content to a web page
– can be alleviated to some extent by using here documents
• Use of an external program requires
• starting a separate process every time an external program is requested
• exchanging data between web server and external program
; resource-intensive
If our main interest is the creation of dynamic web pages,
then the scripting language we use
• should integrate well with HTML
• should not require a web server to execute an external program
COMP284 Scripting Languages Lecture 9 Slide L9 – 3
Overview Features
PHP
• PHP is (now) a recursive acronym for PHP: Hypertext Preprocessor
• Development started in 1994 by Rasmus Lerdorf
• Originally designed as a tool for tracking visitors at Lerdorf’s website
• Developed into full-featured, scripting language for
server-side web programming
• Inherits a lot of the syntax and features from Perl
• Easy-to-use interface to databases
• Free, open-source
• Probably the most widely used server-side web programming language
• Negatives: Inconsistent, muddled API; no scalar objects
The departmental web server uses PHP 5.6.25 (released August 2014)
PHP 7 was released in December 2015 (PHP 6 was never released)
COMP284 Scripting Languages Lecture 9 Slide L9 – 4
Overview Features
PHP processing
• Server plug-ins exist for various web servers
; avoids the need to execute an external program
• PHP code is embedded into HTML pages using tags
; static web pages can easily be turned into dynamic ones
PHP satisfies the criteria we had for a good web scripting language
Processing proceeds as follows:
1 The web server receives a client request
2 The web server recognizes that the client request is for
a HTML page containing PHP code
3 The server executes the PHP code, substitutes output
into the HTML page, the resulting page is then send to the client
As in the case of Perl, the client never sees the PHP code,
only the HTML web page that is produced
COMP284 Scripting Languages Lecture 9 Slide L9 – 5
Overview Applications
PHP: Applications
• Applications written using PHP
• activeCollab – Project Collaboration Software
http://www.activecollab.com/
• Drupal – Content Management System (CMS)
http://drupal.org/home
• Magento – eCommerce platform
http://www.magentocommerce.com/
• MediaWiki – Wiki software
http://www.mediawiki.org/wiki/MediaWiki
• Moodle – Virtual Learning Environment (VLE)
http://moodle.org/
• Sugar – Customer Relationship Management (CRM) platform
http://www.sugarcrm.com/crm/
• WordPress – Blogging tool and CMS
http://wordpress.org/
COMP284 Scripting Languages Lecture 9 Slide L9 – 6
http://www.activecollab.com/
http://drupal.org/home
http://www.magentocommerce.com/
http://www.mediawiki.org/wiki/MediaWiki
http://moodle.org/
http://www.sugarcrm.com/crm/
http://wordpress.org/
Overview Applications
PHP: Websites
• Websites using PHP:
• Delicious – social bookmarking
http://delicious.com/
• Digg – social news website
http://digg.com
• Facebook – social networking
http://www.facebook.com
• Flickr – photo sharing
http://www.flickr.com
• Frienster – social gaming
http://www.frienster.com
• SourceForge – web-based source code repository
http://sourceforge.net/
• Wikipedia – collaboratively built encyclopedia
http://www.wikipedia.org
COMP284 Scripting Languages Lecture 9 Slide L9 – 7
http://delicious.com/
http://digg.com
http://www.facebook.com
http://www.flickr.com
http://www.frienster.com
http://sourceforge.net/
http://www.wikipedia.org
Overview Applications
Recommended texts
• R. Nixon:
Learning PHP, MySQL, and JavaScript.
O’Reilly, 2009.
Harold Cohen Library: 518.561.N73 or e-book
(or later editions of this book)
• M. Achour, F. Betz, A. Dovgal, N. Lopes,
H. Magnusson, G. Richter, D. Seguy, J. Vrana, et al.:
PHP Manual.
PHP Documentation Group, 2018.
http://www.php.net/manual/en/index.php
COMP284 Scripting Languages Lecture 9 Slide L9 – 8
http://www.php.net/manual/en/index.php
Overview Applications
PHP: Hello World!
1
2
3
4
Our first PHP script
5 Hello World!
\n”);
7 ?>
8
• PHP code is enclosed between
• File must be stored in a directory accessible by the web server, for
example $HOME/public_html, and be readable by the web server
• File name must have the extension .php, e.g. hello_world.php
COMP284 Scripting Languages Lecture 9 Slide L9 – 9
Overview Applications
PHP: Hello World!
Since version 4.3.0, PHP also has a command line interface
1 #!/usr/bin/php
2
• PHP code still needs to be enclosed between
• Code must be stored in an executable file
• File name does not need to have any particular format
; PHP can be used as scripting language outside a web programming
context
Output:
Hello World!
COMP284 Scripting Languages Lecture 9 Slide L9 – 10
Overview Applications
PHP: Hello World!
Our first PHP script
Hello World!
\n”);
?>
• Can also ‘executed’ using
php filename
• File does not need to exectuable, only readable for the user
Output:
Our first PHP script
Hello World!
COMP284 Scripting Languages Lecture 9 Slide L9 – 11
Overview Applications
PHP scripts
• PHP scripts are typically embedded into HTML documents and are
enclosed between tags
• A PHP script consists of one or more statements and comments
; there is no need for a main function (or classes)
• Statements end in a semi-colon
• Whitespace before and in between statements is irrelevant
(This does not mean its irrelevant to someone reading your code)
• One-line comments start with // or # and run to the end of the line or ?>
• Multi-line comments are enclosed in /* and */
COMP284 Scripting Languages Lecture 9 Slide L9 – 12
Types and Variables Types
Types
PHP has eight primitive types
• Four scalar types:
• bool – booleans
• int – integers
• float – floating-point numbers
• string – strings
• Two compound types:
• array – arrays
• object – objects
• Two special types:
• resource
• NULL
• Integers, floating-point numbers, and strings do not differ significantly
from the corresponding Perl scalars, including the pecularities of
single-quoted versus double-quoted strings
• In contrast to Perl, PHP does distinguish between different types
including between the four scalar types
COMP284 Scripting Languages Lecture 9 Slide L9 – 13
Types and Variables Variables
Variables
• All PHP variable names start with $ followed by a PHP identifier
• A PHP identifier consists of letters, digits, and underscores,
but cannot start with a digit
PHP identifiers are case sensitive
• In PHP, a variable does not have to be declared before it can be used
• A variable also does not have to be initialised before it can be used,
although initialisation is a good idea
• Uninitialized variables have a default value of their type depending on
the context in which they are used
Type Default Type Default
bool FALSE string empty string
int/float 0 array empty array
If there is no context, then the default value is NULL
COMP284 Scripting Languages Lecture 9 Slide L9 – 14
Types and Variables Variables
Assignments
• Just like Java and Perl, PHP uses the equality sign = for assignments
$student_id = 200846369;
As in Perl, this is an assignment expression
• The value of an assignment expression is the value assigned
$b = ($a = 0) + 1;
// $a has value 0
// $b has value 1
COMP284 Scripting Languages Lecture 9 Slide L9 – 15
Types and Variables Variables
Binary assignments
PHP also supports the standard binary assignment operators:
Binary assignment Equivalent assignment
$a += $b $a = $a + $b
$a -= $b $a = $a – $b
$a *= $b $a = $a * $b
$a /= $b $a = $a / $b
$a %= $b $a = $a % $b
$a **= $b $a = $a ** $b
$a .= $b $a = $a . $b
Example:
// Convert Fahrenheit to Celsius:
// Subtract 32, then multiply by 5, then divide by 9
$temperature = 105; // temperature in Fahrenheit
$temperature -= 32;
$temperature *= 5/9; // converted to Celsius
COMP284 Scripting Languages Lecture 9 Slide L9 – 16
Types and Variables Variables
Constants
• bool define(string, expr [, case_insensitive])
• defines a constant that is globally accessible within a script
• string should be a string consisting of a PHP identifier
(preferably all upper-case)
The PHP identifier is the name of the constant
• expr is an expression that should evaluate to a scalar value
• case_insensitive is an optional boolean argument, indicating
whether the name of the constant is case-insensitive (default is FALSE)
• returns TRUE on success or FALSE on failure
define(“PI” ,3.14159);
define(“SPEED_OF_LIGHT” ,299792458 , true);
COMP284 Scripting Languages Lecture 9 Slide L9 – 17
Types and Variables Variables
Constants
• To use a constant we simply use its name
define(“PI” ,3.14159);
define(“SPEED_OF_LIGHT” ,299792458 , true);
$circumfence = PI * $diameter;
$distance = speed_of_light * $time;
• Caveat: PHP does not resolve constants within double-quoted strings
(or here documents)
print “1 – Value of PI: PI\n”;
print “2 – Value of PI: “.PI.”\n”;
1 – Value of PI: PI
2 – Value of PI: 3.14159
COMP284 Scripting Languages Lecture 9 Slide L9 – 18
Types and Variables Variables
Values, Variables and Types
PHP provides several functions that explore the type of an expression:
string gettype(expr) returns the type of expr as string
bool is_type(expr) checks whether expr is of type type
void var_dump(expr) displays structured information about expr
that includes its type and value
Type of 23: integer
Type of 23.0: double
Type of “23”: string
23 is an integer
COMP284 Scripting Languages Lecture 9 Slide L9 – 19
Types and Variables Type juggling and Type casting
Type juggling and Type casting
• PHP automatically converts a value to the appropriate type as required
by the operation applied to the value (type juggling)
2 . ” worlds” ; “2 worlds”
“2” * 3 ; 6
“1.23e2” + 0 ; 123
“hello” * 3 ; 0
“10hello5” + 5 ; 15
• PHP also supports explicit type casting via (type)
(int) “12” ; 12 (bool) “0” ; FALSE
(int) “1.23e2” ; 1 (bool) “foo” ; TRUE
(int) (“1.23e2” + 0) ; 123 (float) “1.23e2” ; 123
(int) “10hello5” ; 10
(int) 10.5 ; 10
(array) “foo” ; array(0 => “foo”)
COMP284 Scripting Languages Lecture 9 Slide L9 – 20
Types and Variables Comparisons
Comparison operators
Type juggling also plays a role in the way PHP comparison operators work:
expr1 == expr2 Equal TRUE iff expr1 is equal to expr2
after type juggling
expr1 != expr2 Not equal TRUE iff expr1 is not equal to expr2
after type juggling
expr1 <> expr2 Not equal TRUE iff expr1 is not equal to expr2
after type juggling
expr1 === expr2 Identical TRUE iff expr1 is equal to expr2,
and they are of the same type
expr1 !== expr2 Not identical TRUE iff expr1 is not equal to expr2,
or they are not of the same type
Note: For ==, !=, and <>, numerical strings are converted to numbers
and compared numerically
“123” == 123 ; TRUE “123” === 123 ; FALSE
“123” != 123 ; FALSE “123” !== 123 ; TRUE
“1.23e2” == 123 ; TRUE 1.23e2 === 123 ; FALSE
“1.23e2” == “12.3e1” ; TRUE “1.23e2” === “12.3e1” ; FALSE
5 == TRUE ; TRUE 5 === TRUE ; FALSE
COMP284 Scripting Languages Lecture 9 Slide L9 – 21
Types and Variables Comparisons
Comparison operators
Type juggling also plays a role in the way PHP comparison operators work:
expr1 < expr2 Less than TRUE iff expr1 is strictly less than expr2
after type juggling
expr1 > expr2 Greater than TRUE iff expr1 is strictly greater than expr2
after type juggling
expr1 <= expr2 Less than
or equal to
TRUE iff expr1 is less than or equal to expr2
after type juggling
expr1 >= expr2 Greater than
or equal to
TRUE iff expr1 is greater than or equal to expr2
after type juggling
’35.5’ > 35 ; TRUE ’35.5’ >= 35 ; TRUE
’ABD’ > ’ABC’ ; TRUE ’ABD’ >= ’ABC’ ; TRUE
’1.23e2’ > ’12.3e1’ ; FALSE ’1.23e2’ >= ’12.3e1’ ; TRUE
“F1” < "G0" ; TRUE "F1" <= "G0" ; TRUE
TRUE > FALSE ; TRUE TRUE >= FALSE ; TRUE
5 > TRUE ; FALSE 5 >= TRUE ; TRUE
COMP284 Scripting Languages Lecture 9 Slide L9 – 22
Types and Variables Comparisons
Revision
Read
• Chapter 3: Introduction to PHP
of
R. Nixon:
Learning PHP, MySQL, and JavaScript.
O’Reilly, 2009.
Also read
• http://uk.php.net/manual/en/language.types.intro.php
• http://uk.php.net/manual/en/language.types.type-juggling.php
• http://uk.php.net/manual/en/language.operators.comparison.php
• http://uk.php.net/manual/en/types.comparisons.php
COMP284 Scripting Languages Lecture 9 Slide L9 – 23
http://uk.php.net/manual/en/language.types.intro.php
http://uk.php.net/manual/en/language.types.type-juggling.php
http://uk.php.net/manual/en/language.operators.comparison.php
http://uk.php.net/manual/en/types.comparisons.php
Lecture 9
PHP
Motivation
Overview
Features
Applications
Types and Variables
Types
Variables
Type juggling and Type casting
Comparisons