COMP284 Scripting Languages
Lecture 3: PHP (Part 1)
Handouts
Ullrich Hustadt
Department of Computer Science
School of Electrical Engineering, Electronics, and Computer Science
University of Liverpool
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 3 Slide L3 – 2
PHP Motivation
Disadvantages of CGI
•
A distinction is made between static web pages and
dynamic web pages created by external CGI programs
•
Using CGI programs it is difficult to add ‘a little bit’ of
dynamic content to a web page
; can be alleviated to some extent by ‘packing’ big chunks
of HTML markup into a few strings
•
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 3 Slide L3 – 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
•
Shares a lot of the syntax and features with other languages
•
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; compatibility
problems between PHP 5.x and PHP 7.x (PHP 6 was never released)
COMP284 Scripting Languages Lecture 3 Slide L3 – 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 document containing PHP code
3 The server executes the PHP code, substitutes output
into the HTML document, the resulting page is then send to the client
As in the case of CGI programs, the client never sees the PHP code,
only the HTML document that is produced
COMP284 Scripting Languages Lecture 3 Slide L3 – 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 3 Slide L3 – 6
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 3 Slide L3 – 7
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 3 Slide L3 – 8
Overview Applications
PHP: Hello World!
<! DOCTYPE html >
< html lang =" en - GB ">
<head >< title > Hello World </ title ></ head >
<body >
<p > Our first PHP script </ p>
<? php
print ( "<p > <b > Hello World !</b ></p >\ n" );
?>
</ body > </ html >
•
PHP code is enclosed between <?php and ?>
•
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 3 Slide L3 – 9
Overview Applications
PHP: Hello World!
Since version 4.3.0, PHP also has a command line interface
# !/ usr / bin /php
<? php
/* Author : Ullrich Hustadt
A " Hello World " PHP script . */
print ( " Hello World !\ n" );
// A single - line comment
?>
•
PHP code still needs to be enclosed between <?php and ?>
•
Code must be stored in an executable file
•
File name does not need to have any particular format
; PHP can be used to write CGI programs
; PHP can be used as a scripting language outside a web program-
ming context
Output:
Hello World !
COMP284 Scripting Languages Lecture 3 Slide L3 – 10
Overview Applications
PHP: Hello World!
<! DOCTYPE html >
< html lang =" en - GB ">
<head >< title > Hello World </ title ></ head >
<body ><p >Our first PHP script </ p>
<? php
print ( "<p > <b > Hello World !</b ></p >\ n" );
?>
</ body > </ html >
•
Can also be ‘executed’ using
php filenam e
•
File does not need to be exectuable, only readable for the user
Output:
<! DOCTYPE html >
< html lang =" en - GB ">
<head >< title > Hello World </ title ></ head >
<body ><p >Our first PHP script </ p>
<p ><b > Hello World !</b ></p >
</ body > </ html >
COMP284 Scripting Languages Lecture 3 Slide L3 – 11
Overview Applications
PHP scripts
•
PHP scripts are typically embedded into HTML documents and are
enclosed between <?php and ?> 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 3 Slide L3 – 12
Types and Variables Integers and Floating-point numbers
Integers and Floating-point numbers
•
PHP distinguishes between
•
integer numbers 0 2012 -40 1263978
•
floating-point numbers 1.25 256.0 -12e19 2.4e-10
•
PHP supports a wide range of pre-defined mathematical functions
abs(number) absolute value
ceil(number) round fractions up
floor(number) round fractions down
round(number [,prec,mode]) round fractions
log(number [,base]) logarithm
rand(min,max) generate an integer random number
sqrt(number) square root
•
PHP provides pre-defined number constants including
M_PI 3.14159265358979323846
NAN ‘not a number’
INF ‘infinity’
COMP284 Scripting Languages Lecture 3 Slide L3 – 14
Types and Variables Integers and Floating-point numbers
Integers and Floating-point numbers: NAN and INF
The constants NAN and INF are used as return values for some applications
of mathematical functions that do not return a number
•
log(0) returns -INF (negative ‘infinity’)
•
sqrt(-1) returns NAN (‘not a number’)
In PHP 5
•
1/0 returns FALSE and produces a PHP warning
•
0/0 returns FALSE and produces a PHP warning
and execution of the script continues!
In PHP 7
•
1/0 returns INF and produces a PHP warning
•
0/0 returns NAN and produces a PHP warning
and execution of the script continues!
COMP284 Scripting Languages Lecture 3 Slide L3 – 15
Types and Variables Booleans
Booleans
•
PHP has a boolean datatype
with constants TRUE and FALSE (case insensitive)
•
PHP offers the same short-circuit boolean operators as Java and
JavaScript:
&& (conjunction) || (disjunction) ! (negation)
•
Alternatively, and and or can be used instead of && and ||, respectively
•
However, not is not a PHP operator
•
The truth tables for these operators are the same as for JavaScript
•
Remember that && and || are not commutative, that is,
(A && B) is not the same as (B && A)
(A || B) is not the same as (B || A)
COMP284 Scripting Languages Lecture 3 Slide L3 – 16
Types and Variables Booleans
Type conversion to boolean
When converting to boolean, the following values are considered FALSE:
•
the boolean FALSE
•
the integer 0 (zero)
•
the float 0.0 (zero)
•
the string '0' (but not 0.0 nor '00')
•
the empty string ''
•
an array with zero elements
•
an object with zero member variables (PHP 4 only)
•
the special type NULL (including unset variables)
•
SimpleXML objects created from empty tags
Every other value is considered TRUE (including any resource)
When converting a boolean to a string,
•
TRUE becomes "1"
•
FALSE becomes ""
COMP284 Scripting Languages Lecture 3 Slide L3 – 17
Types and Variables Strings
Strings
•
PHP supports both single-quoted and double-quoted strings
•
PHP also supports heredocs as a means to specify multi-line strings
<<< identifier
here d o c u ment
identif i er
•
identifier might optionally be surrounded by double-quotes
•
identifier might also be surrounded by single-quotes,
making the string a nowdoc in PHP terminology
print " < html lang =\" en - GB \" >
<head >< title > Multi - line String </ title > </ head > ";
print < << EOF
<body > Some text
<img alt =" Pi c t u r e of Crown e Plaza " src =" pic . png ">
</ body >
</ html >
EOF ;
COMP284 Scripting Languages Lecture 3 Slide L3 – 18
Types and Variables Strings
Strings
PHP distinguishes between
•
single-quoted strings and
•
double-quoted strings
single-quoted strings double-quoted strings
(‘taken literally’) (‘interpreted’/‘evaluated’)
'hello' ; hello
'don\'t' ; don't
'"hello"' ; "hello"
'backslash\\' ; backslash\
'glass\\table' ; glass\table
'glass\table' ; glass\table
"hello" ; hello
"don't" ; don't
"\"hello\"" ; "hello"
"backslash\\" ; backslash\
"glass\\table" ; glass\table
"glass\table" ; glass able
COMP284 Scripting Languages Lecture 3 Slide L3 – 19
Types and Variables Strings
Strings
•
Variable interpolation is applied to double-quoted strings
$title = " String Opera t ors " ;
print " <title > $title </ title >" ;
<title > String Operators </ title >
•
The string concatenation operator is denoted by ‘.’
•
The string multiplication / repetition operator in PHP is
string str_repeat(string_arg, number)
$string = "<p >I shall not repeat myself .<p >\ n";
print " <body >" . st r_ r epe a t ($ string ,3) . ' </ body > ';
<body ><p >I shall not repeat myself .<p >
<p >I shall not r epeat m yself . <p >
<p >I shall not r epeat m yself . <p >
</ body >
COMP284 Scripting Languages Lecture 3 Slide L3 – 20
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
(Not 100% true, e.g., $uninitialized-- is NULL not -1)
COMP284 Scripting Languages Lecture 3 Slide L3 – 21
Types and Variables Variables
Assignments
•
Just like Java and Python, PHP uses the equality sign =
for assignments
$stude n t_ i d = 20084636 9 ;
As in Java, 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 3 Slide L3 – 22
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
// Convert F ahr e nh e i t to Celsius :
// Subtract 32 , then multiply by 5, then divide by 9
$temp e ra t ur e = 105; // tem p er a tu r e in Fa h ren h eit
$temp e ra t ur e -= 32;
$temp e ra t ur e *= 5;
$temp e ra t ur e /= 9; // conve r t ed to Celsius
COMP284 Scripting Languages Lecture 3 Slide L3 – 23
Types and Variables Variables
Constants
•
bool define(string, expr [, case_insensitive])
•
defines a constant that is globally accessible within a script
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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 value of a scalar type
(In PHP 7, expr can also be an array)
•
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 (" SPEE D_ OF _ LI GH T " ,299792458 , true );
// PHP 7
define (" ANIMALS " ,[" bird "," cat " ," dog " ]);
COMP284 Scripting Languages Lecture 3 Slide L3 – 24
Types and Variables Variables
Constants
•
To use a constant we simply use its name
define (" PI " ,3.14159);
define (" SPEE D_ OF _ LI GH T " ,299792458 , true );
// PHP 7
define (" ANIMALS " ,[" bird "," cat " ," dog " ]);
$circ u mf e nc e = PI * $ d i ame t e r ;
$distance = speed _ of _l ig ht * $time ;
$myPet = ANIMALS [1];
•
Caveat: PHP does not resolve constants within double-quoted strings
(or here documents)
print " 1 - Value of PI: PI \n ";
1 - Value of PI : PI
print " 2 - Value of PI: " . PI . "\ n";
2 - Value of PI : 3.14159
COMP284 Scripting Languages Lecture 3 Slide L3 – 25
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
<? php print ' Type of 23: ' . gettype (23). " \ n";
print ' Type of 23.0: '. gettype (23.0). "\ n";
print ' Type of "23": '. gettype ( " 23 " ). "\n" ;
if ( is_int (23)) { echo " 23 is an integer \ n"; }
else { echo " 23 is not an integer \n " ; }
?>
Type of 23: integer
Type of 23.0: double
Type of " 23 ": string
23 is an integer
COMP284 Scripting Languages Lecture 3 Slide L3 – 26
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 (in PHP 7 also a warning)
"10hello5" + 5 ; 15 (in PHP 7 also a warning)
•
We can apply an identity function of the target type to force a type
conversion
"12" * 1 ; 12 !!1 ; TRUE !!"1" ; TRUE
"12" * 1.0 ; 12.0 !!0 ; FALSE !!"0" ; FALSE
"12.1" * 1 ; 12.1 !!1.0 ; TRUE !!"" ; FALSE
12 . "" ; "12" !!0.0 ; FALSE FALSE . "" ; ""
12.1 . "" ; "12.1" FALSE * 1 ; 0
Conversion of arrays to strings or numbers does not work
COMP284 Scripting Languages Lecture 3 Slide L3 – 27
Type juggling and Type casting
Type juggling and Type casting
•
PHP also supports explicit type casting via (type)
(int) "12" ; 12
(int) "10hello5" ; 10
(int) "1.23e2" ; 1 in PHP 5
(int) "1.23e2" ; 123 in PHP 7
(int) ("1.23e2" * 1) ; 123 in both PHP 5 and 7
(int) (float) "1.23e2" ; 123 in both PHP 5 and 7
(int) "1.23e2h5" ; 1 in PHP 5
(int) "1.23e2h5" ; 123 in PHP 7
(int) 10.5 ; 10
(float) "1.23e2" ; 123.0
(float) "1.23e2h5" ; 123.0
(bool) "0" ; FALSE (was true in JavaScript)
(bool) "foo" ; TRUE
(array) "foo" ; array(0 => "foo")
COMP284 Scripting Languages Lecture 3 Slide L3 – 28
Further Reading
Revision and Further Reading
•
Read
•
Chapter 3: Introduction to PHP
•
Chapter 4: Expressions and Control Flow in PHP: Expressions
of R. Nixon: Learning PHP, MySQL & JavaScript:
with jQuery, CSS & HTML5. O’Reilly, 2018.
•
Read
•
Language Reference: Types: Booleans
http://uk.php.net/manual/en/language.types.boolean.php
•
Language Reference: Types: Integers
http://uk.php.net/manual/en/language.types.integer.php
•
Language Reference: Types: Floating Point Numbers
http://uk.php.net/manual/en/language.types.float.php
•
Language Reference: Types: Strings
http://uk.php.net/manual/en/language.types.string.php
of P. Cowburn (ed.): PHP Manual. The PHP Group, 25 Oct 2019.
http://uk.php.net/manual/en [accessed 26 Oct 2019]
COMP284 Scripting Languages Lecture 3 Slide L3 – 29
