but we cannot characterise both without losing fidelity, for example:

<\w+>.*<\/\w+>

does not capture the ‘pairing’ of HTML tags

COMP284 Scripting Languages Lecture 5 Slide L5 – 2

Regular expressions (2) Capture groups

Regular expressions: Capture groups

The solution are capture groups and backreferences

(regexpr) creates a capture group

(?regexpr) creates a named capture group

(?:regexpr) creates a non-capturing group

\N, \gN, \g{N} backreference to capture group N
(where N is a natural number)

\g{name} backreference to a named capture group

Examples:

1 /Sorting took (\d+\.\d+) seconds/
2 /<(\w+)>.*<\/\1 >/
3 /([A-Z])0{2}(\d+)/
4 /(?\w)(?\w)\g{c2}\g{c1}/
5 /((?\w)(?\w)\g{c2}\g{c1})/

COMP284 Scripting Languages Lecture 5 Slide L5 – 3

Regular expressions (2) Capture groups

Regular expressions: Capture groups

Via capture variables the strings matched by a capture group are also
available outside the pattern in which they are contained

$N string matched by capture group N
(where N is a natural number)

$+{name} string matched by a named capture group

The matched strings are available until the end of the enclosing
code block or until the next successful match

Example:

$_ = “Yabba dabba doo”;

if (/((?\w)(?\w)\g{c2}\g{c1})/) {

print “Match found: $1\n” }

Output:

Match found: abba

COMP284 Scripting Languages Lecture 5 Slide L5 – 4

Regular expressions (2) Alternations

Regular expressions: Alternations

• The regular expression regexpr1|regexpr2 matches
if either regexpr1 or regexpr2 matches
This type of regular expression is called an alternation

• Within a larger regular expression we need to enclose alternations
in a capture group or non-capturing group:
(regexpr1|regexpr2) or (?:regexpr1|regexpr2)

Examples:

1 /Mr|Ms|Mrs|Dr/
2 /cat|dog|bird/
3 /(?: Bill|Hillary) Clinton/

COMP284 Scripting Languages Lecture 5 Slide L5 – 5

Regular expressions (2) Alternations

Regular expressions: Alternations

• The order of expressions in an alternation only matters
if one expression matches a sub-expression of another

Example:

1 $_ = “cats and dogs”;
2 if (/( cat|dog|bird )/) { print “Match 1: $1\n” }
3 if (/( dog|cat|bird )/) { print “Match 2: $1\n” }
4 if (/( dog|dogs )/) { print “Match 3: $1\n” }
5 if (/( dogs|dog )/) { print “Match 4: $1\n” }

Output:

Match 1: cat

Match 2: cat

Match 3: dog

Match 4: dogs

COMP284 Scripting Languages Lecture 5 Slide L5 – 6

Regular expressions (2) Anchors

Regular expressions: Anchors

Anchors allow us to fix where a match has to start or end

\A Match only at string start

^ Match only at string start (default)
Match only at a line start (in //m)

\Z Match only at string end modulo a preceding \n

\z Match only at string end

$ Match only at string end modulo a preceding \n
Match only at a line end (in //m)

\b Match word boundary (between \w and \W)

\B Match except at word boundary

Example:

$_ = “The girl who\nplayed with fire\n”;

if (/fire\z/) { print “‘fire’ at string end\n” }

if (/fire\Z/) { print “‘fire’ at string end modulo \\n\n” }

‘fire’ at string end modulo \n

COMP284 Scripting Languages Lecture 5 Slide L5 – 7

Regular expressions (2) Modifiers

Regular expressions: Modifiers

Modifiers change the interpretation of certain characters in a regular
expression or the way in which Perl finds a match for a regular expression

/ / Default
‘.’ matches any character except ‘\n’
‘^’ matches only at string start
‘$’ matches only at string end modulo preceding \n

/ /s Treat string as a single long line
‘.’ matches any character including ‘\n’
‘^’ matches only at string start
‘$’ matches only at string end modulo preceding \n

/ /m Treat string as a set of multiple lines
‘.’ matches any character except ‘\n’
‘^’ matches at a line start
‘$’ matches at a line end

COMP284 Scripting Languages Lecture 5 Slide L5 – 8

Regular expressions (2) Modifiers

Regular expressions: Modifiers

Modifiers change the interpretation of certain characters in a regular
expression or the way in which Perl finds a match for a regular expression

/ /sm Treat string as a single long line, but detect multiple lines
‘.’ matches any character including ‘\n’
‘^’ matches at a line start
‘$’ matches at a line end

/ /i perform a case-insensitive match

Example:

$_ = “bill\nClinton”;

if (/( Bill|Hillary ). Clinton )/smi) { print “Match: $1\n” }

Output:

Match: bill

Clinton

COMP284 Scripting Languages Lecture 5 Slide L5 – 9

Regular expressions (2) Modifiers

Regular expressions: Modifiers (/ /g and / /c)

Often we want to process all matches for a regular expression,
but the following code has not the desired effect

$_ = “11 22 33”;

while (/\d+/) { print “Match starts at $ -[0]: $&\n” }

The code above does not terminate and endlessly prints out the same text:

Match starts at 0: 11

To obtain the desired behaviour of the while-loop we have to use
the / /g modifier:

/ /g In scalar context, successive invocations against a string will
move from match to match, keeping track of the position in the
string
In list context, returns a list of matched capture groups, or
if there are no capture groups, a list of matches to
the whole regular expression

COMP284 Scripting Languages Lecture 5 Slide L5 – 10

Regular expressions (2) Modifiers

Regular expressions: Modifiers (/ /g and / /c)

With the / /g modifier our code works as desired:

$_ = “11 22 33”;

while (/\d+/g) { print “Match starts at $ -[0]: $&\n” }

Output:

Match starts at 0: 11

Match starts at 3: 22

Match starts at 6: 33

An example in a list context is the following:

$_ = “ab 11 cd 22 ef 33”;

@numbers = (/\d+/g);

print “Numbers: “,join(” | “,@numbers),”\n”;

Output:

Numbers: 11 | 22 | 33

Read / /g as: Start to look for a match from the position where the last
match using / /g ended

COMP284 Scripting Languages Lecture 5 Slide L5 – 11

Regular expressions (2) Modifiers

Regular expressions: Modifiers (/ /g and / /c)

The current position in a string for a regular expression regexpr
is associated with the string, not regexpr
; different regular expressions for the same strings will move forward the

same position when used with / /g

; different strings have different positions and their respective positions
move forward independently

Example:

$_ = “ab 11 cd 22 ef 33”;

if (/\d+/g) { print “Match starts at $-[0]: $&\n” }

if (/[a-z]+/g) { print “Match starts at $-[0]: $&\n” }

if (/\d+/g) { print “Match starts at $-[0]: $&\n” }

Output:

Match starts at 3: 11

Match starts at 6: cd

Match starts at 9: 22

COMP284 Scripting Languages Lecture 5 Slide L5 – 12

Regular expressions (2) Modifiers

Regular expressions: Modifiers (/ /g and / /c)

A failed match or changing the target string resets the position

1 $_ = “ab 11 cd 22 ef 33”;
2 if (/\d+/g) { print “2: Match starts at $-[0]: $&\n” }
3 if (/ab/g) { print “3: Match starts at $-[0]: $&\n” }
4 if (/\d+/g) { print “4: Match starts at $-[0]: $&\n” }

Output:

2: Match starts at 3: 11

4: Match starts at 3: 11

To prevent the reset, an additional modifier / /c can be used

1 $_ = “ab 11 cd 22 ef 33”;
2 if (/\d+/g) { print “2: Match starts at $-[0]: $&\n” }
3 if (/ab/gc) { print “3: Match starts at $-[0]: $&\n” }
4 if (/\d+/g) { print “4: Match starts at $-[0]: $&\n” }

Output:

2: Match starts at 3: 11

4: Match starts at 9: 22

COMP284 Scripting Languages Lecture 5 Slide L5 – 13

Regular expressions (2) Binding operator

Generating regular expressions on-the-fly

The Perl parser will expand occurrences of $variable and @variable
in regular expressions
; regular expessions can be constructed at runtime

Example:

$_ = “Bart teases Lisa”;

@keywords = (“bart”,”lisa”,”marge”,’L\w+’,”t\\w+”);

while ($keyword = shift(@keywords )) {

print “Match found for $keyword: $&\n” if /$keyword/i;

}

Output:

Match found for bart: Bart

Match found for lisa: Lisa

Match found for L\w+: Lisa

Match found for t\w+: teases

COMP284 Scripting Languages Lecture 5 Slide L5 – 14

Regular expressions (2) Binding operator

Binding operator

Perl offers two binding operators for regular expressions

string =∼ /regexpr/ true iff regexpr matches string

string !∼ /regexpr/ true iff regexpr does not match string

• Note that these are similar to comparison operators not assignments
• Most of the time we are not just interested whether these expressions

return true or false, but in the side effect they have on the special
variables $N that store the strings matched by capture groups

Example:

$name = “Dr Ullrich Hustadt”;

if ($name =∼ /(Mr|Ms|Mrs|Dr)?\s*(\w+)/) {print “Hello $2\n”}

$name = “Dave Shield”;

if ($name =∼ /(Mr|Ms|Mrs|Dr)?\s*(\w+)/) {print “Hello $2\n”}

Hello Ullrich

Hello Dave

COMP284 Scripting Languages Lecture 5 Slide L5 – 15

Regular expressions (2) Binding operator

Pattern matching in a list context

• When a pattern match /regexpr/ is used in a list context,
then the return value is

• a list of the strings matched by the capture groups in regexpr
if the match succeeds and regexpr contains capture groups, or

• (a list containing) the value 1
if the match succeeds and regexpr contains no capture groups, or

• an empty list if the match fails

$name = “Dr Ullrich Hustadt”;

($t ,$f ,$l) = ($name =∼ /(Mr|Ms|Mrs|Dr)?\s*(\w+)\s+(\w+)/);

print “Name: $t, $f , $l\n”;

$name = “Dave Shield”;

($t ,$f ,$l) = ($name =∼ /(Mr|Ms|Mrs|Dr)?\s*(\w+)\s+(\w+)/);

print “Name: $t, $f , $l\n”;

Output:

Name: Dr, Ullrich , Hustadt

Name: , Dave , Shield

COMP284 Scripting Languages Lecture 5 Slide L5 – 16

Regular expressions (2) Binding operator

Pattern matching in a list context

• When a pattern match /regexpr/g is used in a list context,
then the return value is

• a list of the strings matched by the capture groups in regexpr
each time regex matches
provided that regexpr contains capture groups, or

• a list containing the string matched by regexpr each time regexpr
matches provided that regexpr contains no capture groups, or

• an empty list if the match fails

$string = “firefox: 10.3 seconds; chrome: 9.5 seconds”;

%performance = ($string =∼ /(\w+)\:\s+(\d+\.\d+)/g);

foreach $system (keys %performance) {

print “$system -> $performance{$system }\n” }

Output:

firefox -> 10.3

chrome -> 9.5

COMP284 Scripting Languages Lecture 5 Slide L5 – 17

Regular expressions (2) Binding operator

Revision

Read

• Chapter 7: In the World of Regular Expressions

• Chapter 8: Matching with Regular Expressions

of

R. L. Schwartz, brian d foy, T. Phoenix:
Learning Perl.
O’Reilly, 2011.

• http://perldoc.perl.org/perlre.html
• http://perldoc.perl.org/perlretut.html
• http://www.perlfect.com/articles/regextutor.shtml

COMP284 Scripting Languages Lecture 5 Slide L5 – 18

http://perldoc.perl.org/perlre.html
http://perldoc.perl.org/perlretut.html
http://www.perlfect.com/articles/regextutor.shtml

COMP284 Scripting Languages
Lecture 6: Perl (Part 5)

Handouts (8 on 1)

Ullrich Hustadt

Department of Computer Science
School of Electrical Engineering, Electronics, and Computer Science

University of Liverpool

Contents

11 Substitution
Binding operators
Capture variables
Modifiers

12 Subroutines
Introduction
Defining a subroutine
Parameters and Arguments
Calling a subroutine
Persistent variables
Nested subroutine definitions

COMP284 Scripting Languages Lecture 6 Slide L6 – 1

Substitution Binding operators

Substitutions

s/regexpr/replacement/

• Searches a variable for a match for regexpr, and if found,
replaces that match with a string specified by replacement

• In both scalar context and list context returns the number of
substitutions made (that is, 0 if no substitutions occur)

• If no variable is specified via one of the binding operators =∼ or !∼,
the special variable $_ is searched and modified

• The binding operator !∼ only negates the return value but does not
affect the manipulation of the text

The delimiter / can be replaced by some other paired or non-paired
character, for example:
s!regexpr!replacement! or s[replacement]

COMP284 Scripting Languages Lecture 6 Slide L6 – 2

Substitution Binding operators

Substitutions

Example:

$text = “http ://www.myorg.co.uk/info/refund /../ vat.html”;

$text =∼ s!/[^\/]+/\.\.!!;

print “$text\n”;

Output:

http :// www.myorg.co.uk/info/vat.html

Example:

$_ = “Yabba dabba doo”;

s/bb/dd/;

print $_ ,”\n”;

Output:

Yadda dabba doo

Note: Only the first match is replaced

COMP284 Scripting Languages Lecture 6 Slide L6 – 3

Substitution Capture variables

Substitutions: Capture variables

s/regexpr/replacement/

• Perl treats replacement like a double-quoted string

; backslash escapes work as in a double-quoted string

\n Newline
\t Tab

\l Lower case next letter
\L Lower case all following letters until \E
\u Upper case next letter
\U Upper case all following letters until \E

; variable interpolation is applied, including capture variables

$N string matched by capture group N
(where N is a natural number)

$+{name} string matched by a named capture group

COMP284 Scripting Languages Lecture 6 Slide L6 – 4

Substitution Capture variables

Substitutions: Capture variables

Example:

$name = “Dr Ullrich Hustadt”;

$name =∼ s/(Mr|Ms|Mrs|Dr)?\s*(\w+)\s+(\w+)/\ U$3\E, $2/;

print “$name\n”;

$name = “Dave Shield”;

$name =∼ s/(Mr|Ms|Mrs|Dr)?\s*(\w+)\s+(\w+)/\ U$3\E, $2/;

print “$name\n”;

Output:

HUSTADT , Ullrich

SHIELD , Dave

COMP284 Scripting Languages Lecture 6 Slide L6 – 5

Substitution Modifiers

Substitutions: Modifiers

Modifiers for substitutions include the following:

s/ / /g Match and replace globally, that is, all occurrences

s/ / /i Case-insensitive pattern matching

s/ / /m Treat string as multiple lines

s/ / /s Treat string as single line

s/ / /e Evaluate the right side as an expression

Combinations of these modifiers are also allowed

Example:

$_ = “Yabba dabba doo”;

s/bb/dd/g;

print $_ ,”\n”;

Output:

Yadda dadda doo

COMP284 Scripting Languages Lecture 6 Slide L6 – 6

Substitution Modifiers

Substitutions: Modifiers

Modifiers for substitutions include the following:

s/ / /e Evaluate the right side as an expression

Example:

1 $text = “The temperature is 105 degrees Fahrenheit”;
2 $text =∼ s!(\d+) degrees Fahrenheit!
3 (($1 -32)*5/9).” degrees Celsius”!e;
4 print “$text\n”;
5 $text =∼ s!(\d+\.\d+)! sprintf(“%d”,$1 +0.5)!e;
6 print “$text\n”;

The temperature is 40.5555555555556 degrees Celsius

The temperature is 41 degrees Celsius

Better:

1 $text = “The temperature is 105 degrees Fahrenheit”;
2 $text =∼ s!(\d+) degrees Fahrenheit!
3 sprintf(“%d” ,(($1 -32)*5/9)+0.5).
4 ” degrees Celsius”!e;

COMP284 Scripting Languages Lecture 6 Slide L6 – 7

Substitution Modifiers

Regular Expressions and the Chomsky Hierarchy

• In Computer Science, formal
languages are categorised
according to the type of grammar
needed to generate them (or the
type of automaton needed to
recognise them)

• Perl regular expressions can
at least recognise all context-free
languages Chomsky Hiearchy of Formal Languages

• Howerver, this does not mean regular expression should be used for
parsing context-free languages

• Instead there are packages specifically for parsing context-free languages
or dealing with specific languages, e.g. HTML, CSV

COMP284 Scripting Languages Lecture 6 Slide L6 – 8

Subroutines Introduction

Java methods versus Perl subroutines

• Java uses methods as a means to encapsulate sequences of instructions
• In Java you are expected
• to declare the type of the return value of a method
• to provide a list of parameters, each with a distinct name,

and to declare the type of each parameter

public static int sum2( int f, int s) {

f = f+s;

return f;

}

public static void main(String [] args) {

System.out.println(“Sum of 3 and 4 is ” + sum2(3, 4));

}

• Instead of methods, Perl uses subroutines

COMP284 Scripting Languages Lecture 6 Slide L6 – 9

Subroutines Defining a subroutine

Subroutines

Subroutines are defined as follows in Perl:

sub identifier {

statements

}

• Subroutines can be placed anywhere in a Perl script but preferably they
should all be placed at start of the script (or at the end of the script)

• All subroutines have a return value (but no declaration of its type)
• The statement
return value

can be used to terminate the execution of a subroutine and
to make value the return value of the subroutine

• If the execution of a subroutine terminates without encountering
a return statement, then the value of the last evaluation of an expression
in the subroutine is returned

The return value does not have to be scalar value, but can be a list

COMP284 Scripting Languages Lecture 6 Slide L6 – 10

Subroutines Parameters and Arguments

Parameters and Arguments

Subroutines are defined as follows in Perl:

sub identifier {

statements

}

• In Perl there is no need to declare the parameters of a subroutine
(or their types)
; there is no pre-defined fixed number of parameters

• Arguments are passed to a subroutine via a special array @_
• Individual arguments are accessed using $_[0], $_[1] etc
• Is is up to the subroutine to process arguments as is appropriate
• The array @_ is private to the subroutine

; each nested subroutine call gets its own @_ array

COMP284 Scripting Languages Lecture 6 Slide L6 – 11

Subroutines Parameters and Arguments

Parameters and Arguments: Examples

• The Java method
public static int sum2( int f, int s) {

f = f+s;

return f;

}

could be defined as follows in Perl:

sub sum2 {

return $_[0] + $_[1];

}

• A more general solution, taking into account that a subroutine can be
given arbitrarily many arguments, is the following:

1 sub sum {
2 return undef if (@_ < 1); 3 $sum = shift(@_); 4 foreach (@_) { $sum += $_ } 5 return $sum; 6 } COMP284 Scripting Languages Lecture 6 Slide L6 – 12 Subroutines Parameters and Arguments Private variables sub sum { return undef if (@_ < 1); $sum = shift(@_); foreach (@_) { $sum += $_ } return $sum; } The variable $sum in the example above is global: $sum = 5; print "Value of \$sum before call of sum: ",$sum ,"\n"; print "Return value of sum: ",&sum(5,4,3,2,1),"\n"; print "Value of \$sum after call of sum: ",$sum ,"\n"; produces the output Value of $sum before call of sum: 5 Return value of sum: 15 Value of $sum after call of sum: 15 This use of global variables in subroutines is often undesirable ; we want $sum to be private/local to the subroutine COMP284 Scripting Languages Lecture 6 Slide L6 – 13 Subroutines Parameters and Arguments Private variables • The operator my declares a variable or list of variables to be private: my $variable; my ($variable1 ,$variable2 ); my @array; • Such a declaration can be combined with a (list) assignment: my $variable = $_[0]; my ($variable1 ,$variable2) = @_; my @array = @_; • Each call of a subroutine will get its own copy of its private variables Example: sub sum { return undef if (@_ < 1); my $sum = shift(@_); foreach (@_) { $sum += $_ } return $sum; } COMP284 Scripting Languages Lecture 6 Slide L6 – 14 Subroutines Calling a subroutine Calling a subroutine A subroutine is called by using the subroutine name with an ampersand & in front possibly followed by a list of arguments The ampersand is optional if a list of arguments is present sub identifier { statements } ... &identifier ... ... &identifier(arguments) ... ... identifier(arguments) ... Examples: print "sum0: " ,&sum ,"\n"; print "sum0: ",sum(),"\n"; print "sum1: ",sum(5),"\n"; print "sum2: ",sum(5,4),"\n"; print "sum5: " ,&sum(5,4,3,2,1),"\n"; $total = sum(9,8,7,6)+sum(5,4,3,2,1); sum(1,2,3,4); COMP284 Scripting Languages Lecture 6 Slide L6 – 15 Subroutines Persistent variables Persistent variables • Private variables within a subroutine are forgotten once a call of the subroutine is completed • In Perl 5.10 and later versions, we can make a variable both private and persistent using the state operator ; the value of a persistent variable will be retained between independent calls of a subroutine Example: use 5.010; sub running_sum { state $sum; foreach (@_) { $sum += $_ } return $sum; } COMP284 Scripting Languages Lecture 6 Slide L6 – 16 Subroutines Persistent variables Persistent variables Example: 1 use 5.010; 2 3 sub running_sum { 4 state $sum; 5 foreach (@_) { $sum += $_ } 6 return $sum; 7 } 8 9 print "running_sum ():\t\t", running_sum (), "\n"; 10 print "running_sum (5):\t", running_sum (5), "\n"; 11 print "running_sum (5 ,4):\t", running_sum (5,4), "\n"; 12 print "running_sum (3,2 ,1):\t",running_sum (3,2,1),"\n"; Output: running_sum (): running_sum (5): 5 running_sum (5 ,4): 14 running_sum (3,2,1): 20 COMP284 Scripting Languages Lecture 6 Slide L6 – 17 Subroutines Nested subroutine definitions Nested subroutine definitions • Perl allows nested subroutine definitions (unlike C or Java) sub outer_sub { sub inner_sub { ... } } • Normally, nested subroutines are a means for information hiding ; the inner subroutine should only be visible and executable from inside the outer subroutine • However, Perl allows inner subroutines to be called from anywhere (within the package in which they are defined) sub outer_sub { sub inner_sub { ... } } inner_sub (); COMP284 Scripting Languages Lecture 6 Slide L6 – 18 Subroutines Nested subroutine definitions Nested subroutine definitions If an inner subroutine uses a local variable of an outer subroutine, then it refers to the instance of that local variable created the first time the outer subroutine was called sub outer { my $x = $_[0]; sub inner { return $x } return inner (); # returns $_[0]? } print "1: ",outer (10),"\n"; print "2: ",outer (20),"\n"; 1: 10 2: 10 # not 20! ; Do not refer to local variables of an outer subroutine, pass information via arguments instead COMP284 Scripting Languages Lecture 6 Slide L6 – 19 Subroutines Nested subroutine definitions Nested subroutine definitions: Example sub sqrt2 { my $x = shift(@_); my $precision = 0.001; sub sqrtIter { my ($guess ,$x) = @_; if (isGoodEnough($guess ,$x)) { return int($guess/$precision +0.5)* $precision; } else { sqrtIter(improveGuess($guess , $x), $x) } } sub improveGuess { my ($guess ,$x) = @_; return ($guess + $x / $guess) / 2; } sub isGoodEnough { my ($guess ,$x) = @_; return (abs($guess * $guess - $x) < $precision ); } return sqrtIter (1.0,$x); } COMP284 Scripting Languages Lecture 6 Slide L6 – 20 Subroutines Nested subroutine definitions Revision Read • Chapter 9: Processing Text with Regular Expressions • Chapter 4: Subroutines of R. L. Schwartz, brian d foy, T. Phoenix: Learning Perl. O’Reilly, 2011. • http://perldoc.perl.org/perlsub.html COMP284 Scripting Languages Lecture 6 Slide L6 – 21 http://perldoc.perl.org/perlsub.html COMP284 Scripting Languages Lecture 7: Perl (Part 6) Handouts (8 on 1) Ullrich Hustadt Department of Computer Science School of Electrical Engineering, Electronics, and Computer Science University of Liverpool Contents 13 Input/Output Filehandles Open Close Read Select Print Here documents 14 Arguments and Options Invocation Arguments Options COMP284 Scripting Languages Lecture 7 Slide L7 – 1 Input/Output Filehandles I/O Connections • Perl programs interact with their environment via I/O connections • A filehandle is the name in a Perl program for such an I/O connection, given by a Perl identifier Beware: Despite the terminology, no files might be involved • There are six pre-defined filehandles STDIN Standard Input, for user input, typically the keyboard STDOUT Standard Output, for user output, typically the terminal STDERR Standard Error, for error output, typically defaults to the terminal DATA Input from data stored after __END__ at the end of a Perl program ARGV Iterates over command-line filenames in @ARGV ARGVOUT Points to the currently open output file when doing edit- in-place processing with -i perl -pi -e ’s/cat/dog/’ file COMP284 Scripting Languages Lecture 7 Slide L7 – 2 Input/Output Filehandles I/O Connections Except for the six predefined I/O connections, all other I/O connections • need to be opened before they can be used open filehandle, mode, expr • should be closed once no longer needed close filehandle • can be used to read from

• can be used to write to
print filehandle list

printf filehandle list

• can be selected as default output
select filehandle

COMP284 Scripting Languages Lecture 7 Slide L7 – 3

Input/Output Filehandles

I/O Connections

Example:

open INPUT , “<", "oldtext.txt" or die "Cannot open file"; open OUTPUT , ">“, “newtext.txt”;

while () {

s!(\d+) degrees Fahrenheit!

sprintf(“%d” ,(($1 -32)*5/9)+0.5).” degrees Celsius”!e;

print OUTPUT;

}

close(INPUT);

close(OUTPUT );

oldtext.txt:

105 degrees Fahrenheit is quite warm

newtext.txt:

41 degrees Celcius is quite warm

COMP284 Scripting Languages Lecture 7 Slide L7 – 4

Input/Output Open

Opening a filehandle

open filehandle, expr

open filehandle, mode, expr

• Opens an I/O connection specified by mode and expr and associates it
with filehandle

• expr specifies a file or command
• mode is one of the following

Mode Operation Create Truncate

< read file > write file yes yes
>> append file yes

+< read/write file +> read/write file yes yes
+>> read/append file yes

|- write to command yes
-! read from command yes

COMP284 Scripting Languages Lecture 7 Slide L7 – 5

Input/Output Close

Closing a filehandle

close

close filehandle

• Flushes the I/O buffer and closes the I/O connection associated with
filehandle

• Returns true if those operations succeed
• Closes the currently selected filehandle if the argument is omitted

COMP284 Scripting Languages Lecture 7 Slide L7 – 6

Input/Output Read

Reading

• In a scalar context, returns a string consisting of all characters from
filehandle up to the next occurrence of $/
(the input record separator)

• In a list context, returns a list of strings representing the whole content
of filehandle separated into string using $/ as a separator
(Default value of $/: newline \n)

1 open INPUT , “<", "oldtext.txt" or die "Cannot open file"; 2 $first_line = ;
3 while ($other_line = ) { … }
4 close INPUT;
5
6 open LS, ” -|”, “ls -1”;
7 @files = ;
8 close LS;
9 foreach $file (@files) { … }

COMP284 Scripting Languages Lecture 7 Slide L7 – 7

Input/Output Select

Selecting a filehandle as default output

select

select filehandle

• If filehandle is supplied, sets the new current default filehandle for
output
; write or print without a filehandle default to filehandle
; References to variables related to output will refer to filehandle

• Returns the currently selected filehandle

COMP284 Scripting Languages Lecture 7 Slide L7 – 8

Input/Output Print

Printing

print filehandle list

print filehandle

print list

print

• Print a string or a list of strings to filehandle
• If filehandle is omitted, prints to the last selected filehandle
• If list is omitted, prints $_
• The current value of $, (if any) is printed between each list item

(Default: undef)

• The current value of $\ (if any) is printed after the entire list has
been printed
(Default: undef)

COMP284 Scripting Languages Lecture 7 Slide L7 – 9

Input/Output Print

Printing: Formatting

sprintf(format, list)

• Returns a string formatted by the usual printf conventions of the C
library function sprintf (but does not by itself print anything)

sprintf “(%10.3f)” 1234.5678

format a floating-point number with minimum width 10 and precision 3
and put the result in parentheses:

( 1234.568)

See http://perldoc.perl.org/functions/sprintf.html for
further details

COMP284 Scripting Languages Lecture 7 Slide L7 – 10

Input/Output Print

Printing: Formatting

printf filehandle format, list

printf format, list

• Equivalent to
print filehandle sprintf(format, list)

except that $\ (the output record separator) is not appended

COMP284 Scripting Languages Lecture 7 Slide L7 – 11

Input/Output Print

Printing: Formatting

Format strings can be stored in variables and can be constructed
on-the-fly:

@list = qw(wilma dino pebbles );

$format = “The items are:\n”. (“%10s\n” x @list );

printf $format , @list;

Output:

The items are:

wilma

dino

pebbles

(The code above uses the ‘quote word’ function qw()
to generate a list of words.
See http://perlmeme.org/howtos/perlfunc/qw_function.html
for details)

COMP284 Scripting Languages Lecture 7 Slide L7 – 12

Input/Output Here documents

Here documents

• A here document is a way of specifying multi-line strings in a scripting
or programming language

• The basic syntax is
<

$title

Lots of HTML markup here

END

The double-quotes in “END”
indicate that everything be-
tween the opening “END” and
the closing END should be
treated like a double-quoted
string

Content -type: text/html

My HTML document

Lots of HTML markup here

COMP284 Scripting Languages Lecture 7 Slide L7 – 14

http://perldoc.perl.org/functions/sprintf.html
http://perlmeme.org/howtos/perlfunc/qw_function.html

Input/Output Here documents

Here documents: Single-quotes

$title = “My HTML document”

print <<’END’; Content -type: text/html

END

The single-quotes in ’END’ indicate that everything between ’END’ and
END should be treated like a single-quoted string
; no variable interpolation is applied
; $title will not be expanded
Content -type: text/html

END

COMP284 Scripting Languages Lecture 7 Slide L7 – 15

Input/Output Here documents

Here documents: Backticks

$command = “ls”;

print <<‘END ‘; $command -1 END The backticks in ‘END‘ tell Perl to run the here document as a shell script (with the here document treated like a double-quoted string) handouts.aux handouts.log handouts.pdf handouts.tex COMP284 Scripting Languages Lecture 7 Slide L7 – 16 Input/Output Here documents Here documents: Variables Here documents can be assigned to variables and manipulated using string operations $header = <<"HEADER"; Content -type: text/html

HEADER

$body = <<"BODY";

$title

Lots of HTML markup here

BODY

$html = $header.$body;

print $html;

COMP284 Scripting Languages Lecture 7 Slide L7 – 17

Arguments and Options Invocation Arguments

Invocation Arguments

• Another way to provide input to a Perl program are
invocation arguments (command-line arguments)

./ perl_program arg1 arg2 arg3

• The invocation arguments given to a Perl program are stored in the
special array @ARGV

perl_program1:

print “Number of arguments: ” ,$#ARGV+1,”\n”;

for ($index =0; $index <= $#ARGV; $index ++) { print "Argument $index: $ARGV[$index],"\n"; } ./ perl_program1 ada ’bob’ 2 Output: Number of arguments: 3 Argument 0: ada Argument 1: bob Argument 2: 2 COMP284 Scripting Languages Lecture 7 Slide L7 – 18 Arguments and Options Options Options • There are various Perl modules that make it easier to process command-line options –scale=5 –debug –file=’image.png’ • One such module is Getopt::Long: http://perldoc.perl.org/Getopt/Long.html • The module provides the GetOptions function • GetOptions parses the command line arguments that are present in @ARGV according to an option specification • Arguments that do not fit to the option specification remain in @ARGV • GetOptions returns true if @ARGV can be processed successfully COMP284 Scripting Languages Lecture 7 Slide L7 – 19 Arguments and Options Options Options: Example perl_program2: use Getopt ::Long; my $file = "photo.jpg"; my $scale = 2; my $debug = 0; $result = GetOptions ("debug" => \$debug , # flag

“scale=i” => \$scale , # numeric

“file=s” => \$file); # string

print “Debug: $debug; Scale: $scale; File: $file\n”;

print “Number of arguments: ” ,$#ARGV+1,”\n”;

print “Arguments: “,join(“,”,@ARGV), “\n”;

./ perl_program2 –scale =5 –file=’image.png’ arg1 arg2

Debug: 0; Scale: 5; File: image.png

Number of arguments: 2

Arguments: arg1 , arg2

COMP284 Scripting Languages Lecture 7 Slide L7 – 20

Arguments and Options Options

Revision

Read

• Chapter 5: Input and Output

of

R. L. Schwartz, brian d foy, T. Phoenix:
Learning Perl.
O’Reilly, 2011.

• http://perldoc.perl.org/perlop.html#I%2fO-Operators
• http://perldoc.perl.org/perlop.html#Quote-Like-Operators
• http://perldoc.perl.org/Getopt/Long.html

COMP284 Scripting Languages Lecture 7 Slide L7 – 21

http://perldoc.perl.org/Getopt/Long.html
http://perldoc.perl.org/perlop.html#I%2fO-Operators
http://perldoc.perl.org/perlop.html#Quote-Like-Operators
http://perldoc.perl.org/Getopt/Long.html

COMP284 Scripting Languages
Lecture 8: Perl (Part 7)

Handouts (8 on 1)

Ullrich Hustadt

Department of Computer Science
School of Electrical Engineering, Electronics, and Computer Science

University of Liverpool

Contents

15 CGI
Overview
CGI I/O

16 The Perl module CGI.pm
Motivation
HTML shortcuts
Forms

COMP284 Scripting Languages Lecture 8 Slide L8 – 1

CGI Overview

Common Gateway Interface — CGI

The Common Gateway Interface (CGI) is a standard method
for web servers to use an external application, 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 8 Slide L8 – 2

CGI CGI I/O

Client requests

In the following we focus on client requests that are generated
using HTML forms

COMP284 Scripting Languages Lecture 8 Slide L8 – 3

CGI CGI I/O

Client requests

In the following we focus on client requests that are generated
using HTML forms

COMP284 Scripting Languages Lecture 8 Slide L8 – 4

CGI CGI I/O

Encoding of input data

• Input data from an HTML form is sent URL-encoded as sequence of
key-value pairs: key1=value1&key2=value2&…

Example:
username=dave&fullname=David%20Davidson

• All characters except A-Z, a-z, 0-9, -, _, ., ∼ (unreserved characters)
are encoded

• ASCII characters that are not unreserved characters are represented
using ASCII codes (preceded by %)

• A space is represented as %20 or +
• + is represented as %2B
• % is represented as %25

Examples:
username=cath&fullname=Catherine+O%27Donnell

COMP284 Scripting Languages Lecture 8 Slide L8 – 5

CGI CGI I/O

Request methods: GET versus POST

The two main request methods used with HTML forms
are GET and POST:

• GET:

• Form data is appended to the URI in the request
“://” “:”

“?”

• Form data is accessed by the CGI program via environment variables

Example:

GET /cgi -bin/cgiwrap/ullrich/demo?username=dave&

fullname=David+Davidson HTTP /1.1

Host: cgi.csc.liv.ac.uk

COMP284 Scripting Languages Lecture 8 Slide L8 – 6

CGI CGI I/O

Request methods: GET versus POST

The two main request methods used with HTML forms are GET and POST:

• POST:

• Form data is appended to end of the request (after headers and blank line) • Form data can be accessed by the CGI program via standard input • Form data is not necessarily URL-encoded (but URL-encoding is the default)

Example:

POST /cgi -bin/cgiwrap/ullrich/demo HTTP /1.1

Host: cgi.csc.liv.ac.uk

username=dave&fullname=David+Davidson

COMP284 Scripting Languages Lecture 8 Slide L8 – 7

CGI CGI I/O

Environment variables: GET

Env variable Meaning

QUERY_STRING The query information passed to the program

REQUEST_METHOD The request method that was used

PATH_INFO Extra path information passed to a CGI program

PATH_TRANSLATED Translation of PATH_INFO from virtual to physical path

SCRIPT_NAME The relative virtual path of the CGI program

SCRIPT_FILENAME The physical path of the CGI program

Example (1): GET http ://cgi.csc.liv.ac.uk/cgi -bin/cgiwrap/ullrich/demo/more/dirs?

username=dave&fullname=David+Davidson

QUERY_STRING username=dave&fullname=David+Davidson

REQUEST_METHOD GET

PATH_INFO /more/dirs

PATH_TRANSLATED /users/www/external/docs/more/dirs

SCRIPT_NAME /cgi -bin/cgiwrap/ullrich/demo

SCRIPT_FILENAME /users/loco/ullrich/public_html/cgi -bin/demo

STDIN

# empty

COMP284 Scripting Languages Lecture 8 Slide L8 – 8

CGI CGI I/O

Environment variables: GET

Env variable Meaning

QUERY_STRING The query information passed to the program

REQUEST_METHOD The request method that was used

PATH_INFO Extra path information passed to a CGI program

PATH_TRANSLATED Translation of PATH_INFO from virtual to physical path

SCRIPT_NAME The relative virtual path of the CGI program

SCRIPT_FILENAME The physical path of the CGI program

Example (2): GET http ://cgi.csc.liv.ac.uk/cgi -bin/cgiwrap/ullrich/demo/more/dirs?

username =2%60n+d%2Bt+e+s%27t&fullname=Peter+Newton

QUERY_STRING username =2%60n+d%2Bt+e+s%27t&fullname=Peter+Newton

REQUEST_METHOD GET

PATH_INFO /more/dirs

PATH_TRANSLATED /users/www/external/docs/more/dirs

SCRIPT_NAME /cgi -bin/cgiwrap/ullrich/demo

SCRIPT_FILENAME /users/loco/ullrich/public_html/cgi -bin/demo

STDIN

# empty

COMP284 Scripting Languages Lecture 8 Slide L8 – 9

CGI CGI I/O

Environment variables: POST

Env variable Meaning

QUERY_STRING The query information passed to the program

REQUEST_METHOD The request method that was used

SCRIPT_NAME The relative virtual path of the CGI program

SCRIPT_FILENAME The physical path of the CGI program

Example: POST /cgi -bin/cgiwrap/ullrich/demo

Host: cgi.csc.liv.ac.uk

username =2%60n+d%2Bt+e+s%27t&fullname=Peter+Newton

QUERY_STRING

# empty

REQUEST_METHOD POST

SCRIPT_NAME /cgi -bin/cgiwrap/ullrich/demo

SCRIPT_FILENAME /users/loco/ullrich/public_html/cgi -bin/demo

STDIN username =2%60n+d%2Bt+e+s%27t&fullname=Peter+Newton

COMP284 Scripting Languages Lecture 8 Slide L8 – 10

CGI CGI I/O

More environment variables

Env variable Meaning

HTTP_ACCEPT A list of the MIME types that the client can accept

HTTP_REFERER The URL of the document that the client points to before accessing the CGI program

HTTP_USER_AGENT The browser the client is using to issue the request

REMOTE_ADDR The remote IP address of the user making the request

REMOTE_HOST The remote hostname of the user making the re- quest

SERVER_NAME The server’s hostname

SERVER_PORT The port number of the host on which the server is running

SERVER_SOFTWARE The name and version of the server software

COMP284 Scripting Languages Lecture 8 Slide L8 – 11

The Perl module CGI.pm Motivation

CGI programs and Perl

• CGI programs need to process input data from environment variables and STDIN, depending on the request method ; preferably, the input data would be accessible by the program

in a uniform way

• CGI programs need to process input data that is encoded ; preferably, the input data would be available in decoded form

• CGI programs need to produce HTML markup/documents as output ; preferably, there would be an easy way to produce HTML markup

In Perl all this can be achieved with the use of the CGI.pm module http://perldoc.perl.org/CGI.html

COMP284 Scripting Languages Lecture 8 Slide L8 – 12

The Perl module CGI.pm HTML shortcuts

CGI.pm HTML shortcuts

• CGI.pm provides so-called HTML shortcuts that create HTML tags

a address applet b body br center code

dd div dl dt em font form

h1 h2 h3 h4 h5 h6 head header

html hr img li ol p pre strong

sup table td th tr title tt ul

• HTML tags have attributes and contents

This is a paragraph

• HTML shortcuts are given • HTML attributes in the form of a hash reference as the first argument • the contents as any subsequent arguments

p({-align=>right},”This is a paragraph”)

COMP284 Scripting Languages Lecture 8 Slide L8 – 13

The Perl module CGI.pm HTML shortcuts

CGI.pm HTML shortcuts: Examples

Code: print p();

Output:

Code: print p(’’);

Output:

Code: print p({-align=>right},”Hello world!”);

Output:

Hello world!

Code: print p({-class=>right_para ,-id=>p1},”Text”);

Output:

Text

COMP284 Scripting Languages Lecture 8 Slide L8 – 14

http://perldoc.perl.org/CGI.html

The Perl module CGI.pm HTML shortcuts

CGI.pm HTML shortcuts: Nesting vs Start/End

• Nested HTML tags using nested HTML shortcuts

Code: print p(em(“Emphasised”).” Text”), “\n”;

Output:

Emphasised Text

• Nested HTML tags using start_tag and end_tag:

use CGI qw(-utf8 :all *em *p);

print start_p(), start_em(), “Emphasised”, end_em(),

” Text”, end_p(), “\n”;

Output:

Emphasised Text

The following start_tag/end_tag HTML shortcuts are generated automatically by CGI.pm:

start_html (), start_form (), start_multipart_form ()

end_html(), end_form () end_multipart_form ()

All others need to be requested by adding *tag to the CGI.pm import list COMP284 Scripting Languages Lecture 8 Slide L8 – 15

The Perl module CGI.pm Forms

CGI.pm Forms

• HTML forms are created using start_form and end_form print start_form ({-method=>request_method ,

-action=>uri});

form_elements

print end_form;

• HTML form elements are again created using HTML shortcuts

textfield textarea password_field

filefield hidden scrolling_list

popup_menu optgroup

image_button checkbox checkbox_group

radio_group reset submit

• optgroup creates an option group within a popup menu ; optgroup occurs nested inside popup_menu

• All other HTML shortcuts for HTML form elements will occur independently of each other within a form

COMP284 Scripting Languages Lecture 8 Slide L8 – 16

The Perl module CGI.pm Forms

CGI.pm Forms: Examples

print textfield ({-name=>’username ’,

-value=>’dave’,

-size=>100,

-maxlength = >500});

• -name specifies the name of the text field and is the only required argument of textfield

• -value specifies a default value that will be shown in the text field • -size is the size of the text field in characters • -maxlength is the maximum number of characters that the text field

will accept

Output:

COMP284 Scripting Languages Lecture 8 Slide L8 – 17

The Perl module CGI.pm Forms

CGI.pm Forms: Examples

print submit({-name=>’submit ’,

-label=>’Click for response ’});

• -name is an optional argument that allows to distinguish submit buttons from each other

• -label or -value is an optional argument that determines the label shown to the user and the value passed to the CGI program

Output:

COMP284 Scripting Languages Lecture 8 Slide L8 – 18

The Perl module CGI.pm Forms

CGI.pm Forms: Example

#!/usr/bin/perl

use CGI qw(-utf8 :all);

print header(-charset=>’utf -8’),

start_html ({-title=>’My HTML Form’,

-author=>’u.hustadt@liverpool.ac.uk’,

-style=>’style.css’});

print start_form ({-method=>”GET”,

-action=>”http :// cgi.csc.liv.ac.uk/”.

“cgi -bin/cgiwrap/ullrich/demo”});

print textfield ({-name=>’username ’,

-value=>’dave’,

-size = >100});

print br();

print textfield ({-name=>’fullname ’,

-value=>’Please enter your name’,

-size = >100});

print br();

print submit({-name=>’submit ’,

-value=>’Click for response ’});

print end_form , end_html;

COMP284 Scripting Languages Lecture 8 Slide L8 – 19

The Perl module CGI.pm Forms

Making it work

For CGI programs to work on our systems you must proceed as follows:

1 Your home directory must be ‘world executable’

2 You must have a directory $HOME/public_html/cgi-bin/

Your public_html and cgi-bin directory must be both readable and executable by everyone

3 Your CGI script must be placed in $HOME/public_html/cgi-bin/

and must be executable by everyone

4 The CGI script can then be accessed using the URL http://cgi.csc.liv.ac.uk/cgi-bin/cgiwrap//

for username, would redirect the browser to malware_site. • Check whether the data has the format expected

if (param(’username ’) !∼ /^[a-zA -Z0 -9]+$/s) {

print "Not a valid user name"

} else {

print "The value of username is ",param(’username ’),"\n";

}

or sanitise the input using the CGI.pm routine escapeHTML:

print "The value of username is ",

escapeHTML(param(’username ’)),"\n";

or even better, do both

COMP284 Scripting Languages Lecture 8 Slide L8 – 25

The Perl module CGI.pm Forms

CGI.pm Scripts: Example (Part 1)

use CGI qw(-utf -8 :all *table);

binmode(STDOUT , ":encoding(utf -8)");

print header(-charset=>’utf -8’), "\n",

start_html ({-title=>’Form Processing ’,

-author=>’u.hustadt@liverpool.ac.uk’});

if (! defined(param(’username ’))) {

# This branch is executed if the user first visits this page/script

print start_form ({-method=>"POST"});

print textfield ({-name=>’username ’, -value=>’dave’,

-size =>100}), "\n";

print br(), "\n";

print textfield ({-name=>’fullname ’,

-value=>’Please enter your name’,

-size =>100}), "\n";

print br(), "\n";

print submit({-name=>’submit ’,

-value=>’Click for response ’}), "\n";

print end_form;

} else {

# This branch is executed if the client request is generated

# by the form

COMP284 Scripting Languages Lecture 8 Slide L8 – 26

The Perl module CGI.pm Forms

CGI.pm Scripts: Example (Part 2)

# (We are in the else -branch now)

print start_table ({-border = >1});

print caption("Inputs");

foreach $key (param ()) {

print Tr(td(’PARAM ’),td($key),td(escapeHTML(param($key ))));

}

foreach $key (keys %ENV) {

print Tr(td(’ENV’),td($key),td(escapeHTML($ENV{$key })));

}

print end_table;

}

print end_html;

COMP284 Scripting Languages Lecture 8 Slide L8 – 27

The Perl module CGI.pm Forms

CGI.pm Scripts: Example (Part 3)

Page produced on the first visit

Page produced on submission of the form

COMP284 Scripting Languages Lecture 8 Slide L8 – 28

The Perl module CGI.pm Forms

Revision

Read

• Chapter 11: Perl Modules

of

R. L. Schwartz, brian d foy, T. Phoenix: Learning Perl. O’Reilly, 2011.

• http://perldoc.perl.org/CGI.html

COMP284 Scripting Languages Lecture 8 Slide L8 – 29

http://perldoc.perl.org/CGI.html

COMP284 Scripting Languages Lecture 9: PHP (Part 1)

Handouts (8 on 1)

Ullrich Hustadt

Department of Computer Science School of Electrical Engineering, Electronics, and Computer Science

University of Liverpool

Contents

17 PHP Motivation

18 Overview Features Applications

19 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

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://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/ 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

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

http://www.php.net/manual/en/index.php

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

COMP284 Scripting Languages Lecture 10: PHP (Part 2)

Handouts (8 on 1)

Ullrich Hustadt

Department of Computer Science School of Electrical Engineering, Electronics, and Computer Science

University of Liverpool

Contents

20 Scalar types Integers and Floating-point numbers Exceptions and error handling Booleans Strings

21 Compound types Arrays Foreach-loops Array functions

22 Printing

COMP284 Scripting Languages Lecture 10 Slide L10 – 1

Scalar types 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 a range of pre-defined number constants including M_PI 3.14159265358979323846 NAN ‘not a number’ INF ‘infinity’

COMP284 Scripting Languages Lecture 10 Slide L10 – 2

Scalar types 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 contrast

• 1/0 returns FALSE and produces an error message • 0/0 returns FALSE and produces an error message and execution of the script continues!

In PHP 7

• 1/0 returns INF and produces an error message • 0/0 returns NAN and produces an error message and execution of the script continues!

COMP284 Scripting Languages Lecture 10 Slide L10 – 3

Scalar types Integers and Floating-point numbers

Integers and Floating-point numbers: NAN and INF

NAN and INF can be compared with each other and other numbers using equality and comparison operators:

NAN == NAN ; FALSE NAN === NAN ; FALSE NAN == 1 ; FALSE INF == INF ; FALSE INF === INF ; TRUE INF == 1 ; FALSE NAN < NAN ; TRUE INF < INF ; TRUE 1 < INF ; TRUE NAN < INF ; TRUE INF < NAN ; TRUE INF < 1 ; FALSE NAN < 1 ; TRUE 1 < NAN ; TRUE In PHP 5.3 and earlier versions, INF == INF returns FALSE In PHP 5.4 and later versions, INF == INF returns TRUE COMP284 Scripting Languages Lecture 10 Slide L10 – 4 Scalar types Integers and Floating-point numbers Integers and Floating-point numbers: NAN and INF • PHP provides three functions to test whether a value is or is not NAN, INF or -INF: • bool is_nan(value) returns TRUE iff value is NAN • bool is_infinite(value) returns TRUE iff value is INF or -INF • bool is_finite(value) returns TRUE iff value is neither NAN nor INF/-INF • In conversion to a boolean value, both NAN and INF are converted to TRUE • In conversion to a string, NAN converts to ’NAN’ and INF converts to ’INF’ COMP284 Scripting Languages Lecture 10 Slide L10 – 5 Scalar types Exceptions and error handling Exceptions and error handling PHP distinguishes between exceptions and errors • A possible way to perform exception handling in PHP is as follows: try { ... run code here ... // try } catch (Exception $e) { ... handle the exception here using $e // catch } • Errors must be dealt with by an error handling function (‘Division by zero’ produces an error not an exception) One possible approach is to let the error handling function turn errors into exceptions function exception_error_handler($errno , $errstr , $errfile , $errline ) { throw new ErrorException($errstr , $errno , 0, $errfile , $errline ); } set_error_handler("exception_error_handler"); http://www.php.net/manual/en/class.errorexception.php COMP284 Scripting Languages Lecture 10 Slide L10 – 6 Scalar types Booleans Booleans • Unlike Perl, PHP does have a boolean datatype with constants TRUE and FALSE (case insensitive) • PHP offers the same short-circuit boolean operators as Java and Perl: && (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 Perl • 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 10 Slide L10 – 7 http://www.php.net/manual/en/class.errorexception.php Scalar types Booleans Type conversion to boolean When converting to boolean, the following values are considered FALSE: • the boolean FALSE itself • the integer 0 (zero) • the float 0.0 (zero) • the empty string, and the string ’0’ • 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) COMP284 Scripting Languages Lecture 10 Slide L10 – 8 Scalar types Strings Strings • PHP supports both single-quoted and double-quoted strings • PHP also supports heredocs as a means to specify multi-line strings The only difference to Perl is the use of <<< instead of << in their definition: <<

’;

print <<Some text

EOF;

COMP284 Scripting Languages Lecture 10 Slide L10 – 9

Scalar types Strings

Strings

• Variable interpolation is applied to double-quoted strings (with slight differences to Perl)

• The string concatenation operator is denoted by ‘.’ (as in Perl) • Instead of Perl’s string multiplication operator ‘x’ there is string str_repeat(string_arg, number)

• There are no built-in HTML shortcuts in PHP

$title = "String Multiplication";

$string = "

I shall not repeat myself.

\n";

print " \n

".str_repeat($string ,3).’’;

I shall not repeat myself.

I shall not repeat myself.

I shall not repeat myself.

COMP284 Scripting Languages Lecture 10 Slide L10 – 10

Compound types Arrays

Arrays

• PHP only supports associative arrays (hashes), simply called arrays • PHP arrays are created using the array construct or,

since PHP 5.4, [ ... ]:

array(key => value , ... )

[key => value , ...]

where key is an integer or string and value can be of any type, including arrays

$arr1 = [1 => "Peter", 3 => 2009, "a" => 101];

$arr2 = array (200846369 => array("name" => "Jan Olsen",

"COMP101" => 69,

"COMP102" => 52));

• The size of an array can be determined using the count function: int count(array [, mode])

print count($arr1); // prints 3

print count($arr2); // prints 1

print count($arr2 ,1); // prints 4

COMP284 Scripting Languages Lecture 10 Slide L10 – 11

Compound types Arrays

Arrays

• It is possible to omit the keys when using the array construct: $arr3 = array("Peter", "Paul", "Mary");

The values given in array will then be associated with the natural numbers 0, 1, . . .

• All the keys of an array can be retrieved using array_keys($array1)

; returns a natural number-indexed array containing the keys of $array1

• All the values of an array can be retrieved using array_values($array1)

; returns a natural number-indexed array containing the values stored in $array1

COMP284 Scripting Languages Lecture 10 Slide L10 – 12

Compound types Arrays

Arrays

• An individual array element can be accessed via its key • Accessing an undefined key produces an error message

and returns NULL

$arr1 = array(1 => "Peter", 3 => 2009, "a"=> 101);

print "’a’: ".$arr1["a"]."\n";

’a’: 101

print "’b’: ".$arr1["b"]."\n";

PHP Notice: Undefined index: b in on line

’b’: // $arr1["b"] returns NULL

$arr1[’b’] = 102;

print "’b’: ".$arr1["b"]."\n";

’b’: 102

COMP284 Scripting Languages Lecture 10 Slide L10 – 13

Compound types Arrays

Arrays

• PHP allows the construct $array[] = value;

PHP will determine the maximum value M among the integer indices in $array and use the key K = M + 1; if there are no integer indices in $array, then K = 0 will be used ; auto-increment for array keys

$arr4 [] = 51; // 0 => 51

$arr4 [] = 42; // 1 => 42

$arr4 [] = 33; // 2 => 33

• A key-value pair can be removed from an array using the unset function:

$arr1 = array(1 => "Peter", 3 => 2009, "a" => 101);

unset($arr1 [3]); // Removes the pair 3 => 2009

unset($arr1 ); // Removes the whole array

COMP284 Scripting Languages Lecture 10 Slide L10 – 14

Compound types Foreach-loops

Arrays: foreach-loop

• PHP provides a foreach-loop construct to ‘loop’ through the elements of an array

• Syntax and semantics is slightly different from that of the corresponding construct in Perl

foreach (array as $value)

statement

foreach (array as $key => $value)

statement

• array is an array expression • $key and $value are two variables, storing a different key-value pair in array at each iteration of the foreach-loop

• We call $value the foreach-variable • foreach iterates through an array in the order in which elements were

defined

COMP284 Scripting Languages Lecture 10 Slide L10 – 15

Compound types Foreach-loops

Arrays: foreach-loop

foreach iterates through an array in the order in which elements were defined

Example 1: foreach (array("Peter", "Paul", "Mary") as $key => $value)

print "The array maps $key to $value\n";

The array maps 0 to Peter

The array maps 1 to Paul

The array maps 2 to Mary

Example 2: $arr5 [2] = "Marry";

$arr5 [0] = "Peter";

$arr5 [1] = "Paul";

// 0 => ’Peter ’, 1 => ’Paul ’, 2 => ’Marry ’

foreach ($arr5 as $key => $value)

print "The array maps $key to $value\n";

The array maps 2 to Mary

The array maps 0 to Peter

The array maps 1 to Paul

COMP284 Scripting Languages Lecture 10 Slide L10 – 16

Compound types Foreach-loops

Arrays: foreach-loop

Does changing the value of the foreach-variable change the element of the list that it currently stores?

Example 3:

$arr6 = array("name" => "Peter", "year" => 2009);

foreach ($arr6 as $key => $value) {

print "The array maps $key to $value\n";

$value .= " - modified"; // Changing $value

}

print "\n";

foreach ($arr6 as $key => $value)

print "The array now maps $key to $value\n";

The array maps name to Peter

The array maps year to 2009

The array now maps name to Peter

The array now maps year to 2009

COMP284 Scripting Languages Lecture 10 Slide L10 – 17

Compound types Foreach-loops

Arrays: foreach-loop

• In order to modify array elements within a foreach-loop we need use a reference

foreach (array as &$value)

statement

unset($value);

foreach (array as $key => &$value)

statement

unset($value);

• In the code schemata above, &$value is a variable whose value is stored at the same location as an array element

• Note that PHP does not allow the key to be a reference • The unset statement is important to return $value to being a ‘normal’

variable

COMP284 Scripting Languages Lecture 10 Slide L10 – 18

Compound types Foreach-loops

Arrays: foreach-loop

In order to modify array elements within a foreach-loop we need use a reference

Example:

$arr6 = array("name" => "Peter", "year" => 2009);

foreach ($arr6 as $key => &$value) { // Note: reference!

print "The array maps $key to $value\n";

$value .= " - modified";

}

unset($value ); // Remove the reference from $value

print "\n";

foreach ($arr6 as $key => $value)

print "The array now maps $key to $value\n";

The array maps name to Peter

The array maps year to 2009

The array now maps name to Peter - modified

The array now maps year to 2009 - modified

COMP284 Scripting Languages Lecture 10 Slide L10 – 19

Compound types Array functions

Array functions

PHP has no stack or queue data structures, but has stack and queue functions for arrays:

• array_push($array, value1, value2,...) appends one or more elements at the end of the end of an array variable; returns the number of elements in the resulting array

• array_pop($array) extracts the last element from an array and returns it

• array_shift($array) shift extracts the first element of an array and returns it

• array_unshift($array, value1, value2,...) inserts one or more elements at the start of an array variable; returns the number of elements in the resulting array

Note: $array needs to be a variable

COMP284 Scripting Languages Lecture 10 Slide L10 – 20

Printing

Printing

In PHP, the default command for generating output is echo

• void echo(arg1) void echo arg1, arg2, ...

• Outputs all arguments • No parentheses are allowed if there is more than one argument • More efficient than print (and therefore preferred)

Additionally, PHP also provides the functions print, and printf:

• int print(arg)

• Outputs its argument Only one argument is allowed!

• Returns value 1 • Parentheses can be omitted

COMP284 Scripting Languages Lecture 10 Slide L10 – 21

Printing

Printing

• string sprintf(format, arg1, arg2, ....) • Returns a string produced according to the formatting string format • Parentheses are necessary

See http://www.php.net/manual/en/function.sprintf.php for details

• int printf(format, arg1, arg2, ...)

• Produces output according to format • Parentheses are necessary • Returns the length of the outputted string

• Important: In contrast to Perl, a PHP array cannot take the place of a list of arguments

printf("%2d apples %2d oranges\n",array (5 ,7));

produces an error message

COMP284 Scripting Languages Lecture 10 Slide L10 – 22

Printing

Printing

• string vsprintf(format, array) • Returns a string produced according to the formatting string format • Identical to sprintf but accepts an array as argument • Parentheses are necessary

• int vprintf(format, array) • Produces output according to format • Identical to printf but accepts an array as argument • Parentheses are necessary

vprintf("%2d apples %2d oranges\n",array (5 ,7));

5 apples 7 oranges

COMP284 Scripting Languages Lecture 10 Slide L10 – 23

http://www.php.net/manual/en/function.sprintf.php

Printing

Revision

Read

• Chapter 6: PHP Arrays

of

R. Nixon: Learning PHP, MySQL, and JavaScript. O’Reilly, 2009.

• http://uk.php.net/manual/en/language.types.boolean.php • http://uk.php.net/manual/en/language.types.integer.php • http://uk.php.net/manual/en/language.types.float.php • http://uk.php.net/manual/en/language.types.string.php • http://uk.php.net/manual/en/language.types.array.php • http://uk.php.net/manual/en/control-structures.foreach.php

COMP284 Scripting Languages Lecture 10 Slide L10 – 24

http://uk.php.net/manual/en/language.types.boolean.php http://uk.php.net/manual/en/language.types.integer.php http://uk.php.net/manual/en/language.types.float.php http://uk.php.net/manual/en/language.types.string.php http://uk.php.net/manual/en/language.types.array.php http://uk.php.net/manual/en/control-structures.foreach.php

COMP284 Scripting Languages Lecture 11: PHP (Part 3)

Handouts (8 on 1)

Ullrich Hustadt

Department of Computer Science School of Electrical Engineering, Electronics, and Computer Science

University of Liverpool

Contents

23 Special types NULL Resources

24 Control structures Conditional statements Switch statements While- and Do While-loops For-loops

25 Functions Defining a function Calling a function Variables Functions and HTML Variable-length argument lists

26 PHP libraries Include/Require

COMP284 Scripting Languages Lecture 11 Slide L11 – 1

Special types NULL

NULL

• NULL is both a special type and a value • NULL is the only value of type NULL

and the name of this constant is case-insensitive

• A variable has both type NULL and value NULL in the following three situations:

1 The variable has not yet been assigned a value (not equal to NULL) 2 The variable has been assigned the value NULL 3 The variable has been unset using the unset operation

• There are a variety of functions that can be used to test whether a variable is NULL including:

• bool isset($variable) TRUE iff $variable exists and does not have value NULL

• bool is_null(expr) TRUE iff expr is identical to NULL

COMP284 Scripting Languages Lecture 11 Slide L11 – 2

Special types NULL

NULL

Warning: Using NULL with == may lead to counter-intuitive results

$d = array();

echo var_dump($d), "\n";

array(0) {

}

echo ’is_null($d): ’, (is_null($d)) ? "TRUE\n": "FALSE\n";

is_null($d): FALSE

echo ’$d === null: ’, ($d === null) ? "TRUE\n": "FALSE\n";

$d === null: FALSE

echo ’$d == null: ’, ($d == null) ? "TRUE\n": "FALSE\n";

$d == null: TRUE

Type juggling means that an empty array is (loosely) equal to NULL but not identical (strictly equal) to NULL

COMP284 Scripting Languages Lecture 11 Slide L11 – 3

Special types Resources

Resources

A resource is a reference to an external resource and corresponds to a Perl filehandle

• resource fopen(filename, mode) Returns a file pointer resource for filename access using mode on success, or FALSE on error

Mode Operation Create Truncate

’r’ read file ’r+’ read/write file ’w’ write file yes yes ’w+’ read/write file yes yes ’a’ append file yes ’a+’ read/append file yes ’x’ write file yes ’x+’ read/write file yes

See http://www.php.net/manual/en/resource.php for further details

COMP284 Scripting Languages Lecture 11 Slide L11 – 4

Special types Resources

Resources

• bool fclose(resource) • Closes the resource • Returns TRUE on success

• string fgets(resource [, length]) • Returns a line read from resource and

returns FALSE if there is no more data to be read

• With optional argument length, reading ends when length− 1 bytes have been read, or a newline or on EOF (whichever comes first)

• string fread(resource,length) • Returns length characters read from resource

$handle = fopen(’somefile.txt’, ’r’);

while ($line = fgets($handle )) {

// processing the line of the file

}

fclose($handle );

COMP284 Scripting Languages Lecture 11 Slide L11 – 5

Special types Resources

Resources

• int fwrite(resource, string [, length]) • Writes a string to a resource • If length is given, writing stops after length bytes have been written or the

end of string is reached, whichever comes first

• int fprintf(resource, format, arg1, arg2, ...) • Writes a list of arguments to a resource in the given format • Identical to fprintf with output to resource

• int vfprintf (resource, format, array) • Writes the elements of an array to a resource in the given format • Identical to vprintf with output to resource

$handle = fopen(’somefile.txt’, ’w’);

fwrite($handle ,"Hello World!".PHP_EOL ); // ‘logical newline ’

fclose($handle );

In contrast to Perl, in PHP \n always represents the character with ASCII code 10 not the platform dependent newline ; use PHP_EOL instead

COMP284 Scripting Languages Lecture 11 Slide L11 – 6

Control structures Conditional statements

Control structures: conditional statements

The general format of conditional statements is very similar but not identical to that in Java and Perl:

if (condition) {

statements

} elseif (condition) {

statements

} else {

statements

}

• the elseif-clauses is optional and there can be more than one Note: elseif instead of elsif!

• the else-clause is optional but there can be at most one • in contrast to Perl, the curly brackets can be omitted if there is only

a single statement in a clause

COMP284 Scripting Languages Lecture 11 Slide L11 – 7

http://www.php.net/manual/en/resource.php

Control structures Conditional statements

Control structures: conditional statements/expressions

• PHP allows to replace curly brackets with a colon : combined with an endif at the end of the statement:

if (condition ):

statements

elseif (condition ):

statements

else:

statements

endif

This also works for the switch statement in PHP

However, this syntax becomes difficult to parse when nested conditional statements are used and is best avoided

• PHP also supports conditional expressions condition ? if_true_expr : if_false_expr

COMP284 Scripting Languages Lecture 11 Slide L11 – 8

Control structures Switch statements

Control structures: switch statement

A switch statement in PHP takes the following form

switch (expr) {

case expr1:

statements

break;

case expr2:

statements

break;

default:

statements

break;

}

• there can be arbitrarily many case-clauses • the default-clause is optional but there can be

at most one

• expr is evaluated only once and then compared to expr1, expr2, etc using (loose) equality ==

• once two expressions are found to be equal the corresponing clause is executed

• if none of expr1, expr2, etc are equal to expr, then the default-clause will be executed

• break ‘breaks out’ of the switch statement • if a clause does not contain a break command,

then execution moves to the next clause

COMP284 Scripting Languages Lecture 11 Slide L11 – 9

Control structures Switch statements

Control structures: switch statement

Example:

switch ($command) {

case "North":

$y += 1; break;

case "South":

$y -= 1; break;

case "West";

$x -= 1; break;

case "East":

$x += 1; break;

case "Search":

if (($x = 5) && ($y = 3))

echo "Found a treasure\n";

else

echo "Nothing here\n";

break;

default:

echo "Not a valid command\n"; break;

}

COMP284 Scripting Languages Lecture 11 Slide L11 – 10

Control structures Switch statements

Control structures: switch statement

Not every case-clause needs to have associated statements

Example: switch ($month) {

case 1: case 3: case 5: case 7:

case 8: case 10: case 12:

$days = 31;

break;

case 4: case 6: case 9: case 11:

$days = 30;

break;

case 2:

$days = 28;

break;

default:

$days = 0;

break;

}

COMP284 Scripting Languages Lecture 11 Slide L11 – 11

Control structures While- and Do While-loops

Control structures: while- and do while-loops

• PHP offers while-loops and do while-loops while (condition) {

statements

}

do {

statements

} while (condition );

• As usual, curly brackets can be omitted if the loop consists of only one statement

Example:

// Compute the factorial of $number

$factorial = 1;

do {

$factorial *= $number --;

} while ($number > 0);

COMP284 Scripting Languages Lecture 11 Slide L11 – 12

Control structures For-loops

Control structures: for-loops

• for-loops in PHP take the form

for (initialisation; test; increment) {

statements

}

Again, the curly brackets are not required if the body of the loop only consists of a single statement

• In PHP initialisation and increment can consist of more than one statement, separated by commas instead of semicolons

Example:

for ($i = 3, $j = 3; $j >= 0; $i++, $j --)

echo "$i - $j - ", $i*$j, "\n";

3 - 3 - 9

4 - 2 - 8

5 - 1 - 5

6 - 0 - 0

COMP284 Scripting Languages Lecture 11 Slide L11 – 13

Control structures For-loops

Control structures: break and continue

• The break command can also be used in while-, do while-, and for-loops and discontinues the execution of the loop

while ($value = array_shift($data) {

$written = fwrite($resource ,$value );

if (! $written) break;

}

• The continue command stops the execution of the current iteration of a loop and moves the execution to the next iteration

for ($x = -2; $x <= 2; $x++) { if ($x == 0) continue; printf("10 / %2d = %3d\n",$x ,(10/ $x)); } 10 / -2 = -5 10 / -1 = -10 10 / 1 = 10 10 / 2 = 5 COMP284 Scripting Languages Lecture 11 Slide L11 – 14 Functions Defining a function Functions Functions are defined as follows in PHP: function identifier($param1 ,&$param2 , ...) { statements } • Functions can be placed anywhere in a PHP script but preferably they should all be placed at start of the script (or at the end of the script) • Function names are case-insensitive • The function name must be followed by parentheses • A function has zero, one, or more parameters that are variables • Parameters can be given a default value using $param = const_expr • When using default values, any defaults must be on the right side of any parameters without defaults COMP284 Scripting Languages Lecture 11 Slide L11 – 15 Functions Defining a function Functions Functions are defined as follows in PHP: function identifier($param1 ,&$param2 , ...) { statements } • The return statement return value can be used to terminate the execution of a function and to make value the return value of the function • The return value does not have to be scalar value • A function can contain more than one return statement • Different return statements can return values of different types COMP284 Scripting Languages Lecture 11 Slide L11 – 16 Functions Calling a function Calling a function A function is called by using the function name followed by a list of arguments in parentheses function identifier($param1 , &$param2 , ...) { ... } ... identifier(arg1 , arg2 ,...) ... • The list of arguments can be shorter as well as longer as the list of parameters • If it is shorter, then default values must have been specified for the parameters without corresponding arguments Example: function sum($num1 ,$num2) { return $num1+$num2; } echo "sum: ",sum(5,4),"\n"; $sum = sum (3 ,2); COMP284 Scripting Languages Lecture 11 Slide L11 – 17 Functions Variables Variables PHP distinguishes three categories of variables: • Local variables are only accessible in the part of the code in which they are introduced • Global variables are accessible everywhere in the code • Static variables are local variables within a function that retain their value between separate calls of the function By default, variables in PHP are local but not static (Variables in Perl are by default global) COMP284 Scripting Languages Lecture 11 Slide L11 – 18 Functions Variables PHP functions: Example function bubble_sort($array) { // $array , $size , $i, $j are all local if (! is_array($array )) trigger_error("Argument not an array\n", E_USER_ERROR ); $size = count($array ); for ($i=0; $i <$size; $i++) { for ($j=0; $j <$size -1-$i; $j++) { if ($array[$j+1] < $array[$j]) { swap($array , $j, $j+1); } } } return $array; } function swap(&$array , $i, $j) { // swap expects a reference (to an array) $tmp = $array[$i]; $array[$i] = $array[$j]; $array[$j] = $tmp; } COMP284 Scripting Languages Lecture 11 Slide L11 – 19 Functions Variables PHP functions: Example function bubble_sort($array) { ... swap($array , $j , $j+1); ... return $array; } function swap(&$array , $i, $j) { $tmp = $array[$i]; $array[$i] = $array[$j]; $array[$j] = $tmp; } $array = array (2,4,3,9,6,8,5,1); echo "Before sorting ", join(", ",$array), "\n"; $sorted = bubble_sort($array ); echo "After sorting ", join(", ",$array), "\n"; echo "Sorted array ", join(", ",$sorted), "\n"; Before sorting 2, 4, 3, 9, 6, 8, 5, 1 After sorting 2, 4, 3, 9, 6, 8, 5, 1 Sorted array 1, 2, 3, 4, 5, 6, 8, 9 COMP284 Scripting Languages Lecture 11 Slide L11 – 20 Functions Variables Functions and global variables • A variable is declared to be global using the keyword global function echo_x($x) { echo $x," "; global $x; echo $x; } $x = 5; // this is a global variable called $x echo_x (10); // prints first ‘10’ then ‘5’ ; an otherwise local variable is made accessible outside its normal scope using global ; all global variables with the same name refer to the same storage location/data structure ; an unset operation removes a specific variable, but leaves other (global) variables with the same name unchanged COMP284 Scripting Languages Lecture 11 Slide L11 – 21 Functions Variables PHP functions and Global variables function modify_or_destroy_var($arg) { global $x , $y; if (is_bool($arg) && !$arg) { $x = $x * $y; } if (is_bool($arg) && $arg) { unset($x); echo $x; } } $x = 2; $y = 3; $z = 4; echo "1: \$x = $x, \$y = $y, \$z = $z\n"; 1: $x = 2, $y = 3, $z = 4 unset($z); echo "2: \$x = $x, \$y = $y, \$z = $z\n"; PHP Notice: Undefined variable: z in script on line 9 2: $x = 2, $y = 3, $z = modify_or_destroy_var(false ); echo "3: \$x = $x, \$y = $y\n"; 3: $x = 6, $y = 3 modify_or_destroy_var(true); echo "4: \$x = $x, \$y = $y\n"; PHP Notice: Undefined variable: x in script on line 4 4: $x = 6, $y = 3 COMP284 Scripting Languages Lecture 11 Slide L11 – 22 Functions Variables PHP functions and Static variables • A variable is declared to be static using the keyword static and should be combined with the assignment of an initial value (initialisation) function counter () { static $count = 0; return $count ++; } ; static variables are initialised only once 1 function counter () { static $count = 0; return $count ++; } 2 $count = 5; 3 echo "1: global \$count = $count\n"; 4 echo "2: static \$count = ",counter(),"\n"; 5 echo "3: static \$count = ",counter(),"\n"; 6 echo "4: global \$count = $count\n"; 1: global $count = 5 2: static $count = 0 3: static $count = 1 4: global $count = 5 COMP284 Scripting Languages Lecture 11 Slide L11 – 23 Functions Functions and HTML Functions and HTML • It is possible to include HTML markup in the body of a function definition • The HTML markup can in turn contain PHP scripts • A call of the function will execute the PHP scripts, insert the output into the HTML markup, then output the resulting HTML markup

COMP284 Scripting Languages Lecture 11 Slide L11 – 24

Functions Variable-length argument lists

Functions with variable number of arguments

The number of arguments in a function call is allowed to exceed the number of its parameters ; the parameter list only specifies the minimum number of arguments

• int func_num_args() returns the number of arguments passed to a function

• mixed func_get_arg(arg_num) returns the specified argument, or FALSE on error

• array func_get_args() returns an array with copies of the arguments passed to a function

function sum() { // no minimum number of arguments

if (func_num_args () < 1) return null; $sum = 0; foreach (func_get_args () as $value) { $sum += $value; } return $sum; } COMP284 Scripting Languages Lecture 11 Slide L11 – 25 PHP libraries Include/Require Including and requiring files • It is often convenient to build up libraries of function definitions, stored in one or more files, that are then reused in PHP scripts • PHP provides the commands include, include_once, require, and require_once to incorporate the content of a file into a PHP script include ’mylibrary.php’; • PHP code in a library file must be enclosed within a PHP start tag

• The incorporated content inherits the scope of the line in which an include command occurs

• If no absolute or relative path is specified, PHP will search for the file • first, in the directories in the include path include_path • second, in the script’s directory • third, in the current working directory

COMP284 Scripting Languages Lecture 11 Slide L11 – 26

PHP libraries Include/Require

Including and requiring files

• Several include or require commands for the same library file results in the file being incorporated several times ; defining a function more than once results in an error

• Several include_once or require_once commands for the same library file results in the file being incorporated only once

• If a library file requested by include and include_once cannot be found, PHP generates a warning but continues the execution of the requesting script

• If a library file requested by require and require_once cannot be found, PHP generates a error and stops execution of the requesting script

COMP284 Scripting Languages Lecture 11 Slide L11 – 27

PHP libraries Include/Require

PHP Libraries: Example

mylibrary.php

example.php

COMP284 Scripting Languages Lecture 11 Slide L11 – 28

PHP libraries Include/Require

Revision

Read

• Chapter 4: Expressions and Control Flow in PHP • Chapter 5: PHP Functions and Objects • Chapter 7: Practical PHP of

R. Nixon: Learning PHP, MySQL, and JavaScript. O’Reilly, 2009.

• http://uk.php.net/manual/en/language.control-structures.php • http://uk.php.net/manual/en/language.functions.php • http://uk.php.net/manual/en/function.include.php • http://uk.php.net/manual/en/function.include-once.php • http://uk.php.net/manual/en/function.require.php • http://uk.php.net/manual/en/function.require-once.php

COMP284 Scripting Languages Lecture 11 Slide L11 – 29

http://uk.php.net/manual/en/language.control-structures.php http://uk.php.net/manual/en/language.functions.php http://uk.php.net/manual/en/function.include.php http://uk.php.net/manual/en/function.include-once.php http://uk.php.net/manual/en/function.require.php http://uk.php.net/manual/en/function.require-once.php

COMP284 Scripting Languages Lecture 12: PHP (Part 4)

Handouts (8 on 1)

Ullrich Hustadt

Department of Computer Science School of Electrical Engineering, Electronics, and Computer Science

University of Liverpool

Contents 27 Web applications

Overview HTML forms

28 Available information and Input Overview PHP environment Server variables Form data

29 PHP sessions Start a PHP session Maintain session data End a PHP session Session management Example

30 Authentication Overview Example

COMP284 Scripting Languages Lecture 12 Slide L12 – 1

Web applications Overview

Web applications using PHP

IBM: Build Ajax-based Web sites with PHP, 2 Sep 2008. https://www.ibm.com/developerworks/library/wa-aj-php/ [accessed 6 Mar 2013]

COMP284 Scripting Languages Lecture 12 Slide L12 – 2

Web applications HTML forms

HTML forms

When considering Perl CGI programming we have used HTML forms that generated a client request that was handled by a Perl CGI program:

Now we will use a PHP script instead:

• The PHP script file must be stored in a directory accessible by the web server, for example $HOME/public_html, and be readable by the web server

• The PHP script file name must have the extension .php, e.g. demo.php

COMP284 Scripting Languages Lecture 12 Slide L12 – 3

Available information and Input Overview

Information available to PHP scripts

• Information about the PHP environment

• Information about the web server and client request

• Information stored in files and datbases • Form data

• Cookie/Session data

• Miscellaneous • string date(format)

returns the current date/time presented according to format for example, date(’H:i l, j F Y’)

results in 12:20 Thursday, 8 March 2012 (See http://www.php.net/manual/en/function.date.php)

• int time() returns the current time measured in the number of seconds since January 1 1970 00:00:00 GMT

COMP284 Scripting Languages Lecture 12 Slide L12 – 4

Available information and Input PHP environment

PHP environment

• phpinfo() displays information about the PHP installation and EGPCS data (Environment, GET, POST, Cookie, and Server data) for the current client request

• phpinfo(part) displays selected information

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/phpinfo.php

INFO_GENERAL The configuration, php.ini location, build date, web server

INFO_CONFIGURATION Local and master values for PHP directives INFO_MODULES Loaded modules INFO_VARIABLES All EGPCS data

COMP284 Scripting Languages Lecture 12 Slide L12 – 5

Available information and Input PHP environment

Manipulating the PHP configuration

The following functions can be used to access and change the configuation of PHP from within a PHP script:

• array ini_get_all() • returns all the registered configuration options

• string ini_get(option) • returns the value of the configuration option on success

• string ini_set(option, value) • sets the value of the given configuration option to a new value • the configuration option will keep this new value during the script’s

execution and will be restored afterwards

• void ini_restore(option) • restores a given configuration option to its original value

COMP284 Scripting Languages Lecture 12 Slide L12 – 6

Available information and Input Server variables

Server variables

The $_SERVER array stores information about the web server and the client request

; Similar to %ENV for Perl CGI programs

’;

echo ’Remote address: ’,$_SERVER[’REMOTE_ADDR ’], ’
’;

echo ’Client browser: ’,$_SERVER[’HTTP_USER_AGENT ’],’
’;

echo ’Request method: ’,$_SERVER[’REQUEST_METHOD ’];

?>

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/server.php

Server software: Apache /2.2.22 (Fedora)

Remote address: 10.128.0.215

Client browser: Mozilla /5.0 ... Chrome /41.0.2272.53 ...

Request method:

See http://php.net/manual/en/reserved.variables.server.php for a list of keys

COMP284 Scripting Languages Lecture 12 Slide L12 – 7

https://www.ibm.com/developerworks/library/wa-aj-php/ http://www.php.net/manual/en/function.date.php http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/phpinfo.php http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/server.php http://php.net/manual/en/reserved.variables.server.php

Available information and Input Form data

Form data

• Form data is passed to a PHP script via the three arrays: $_POST Data from POST client requests $_GET Data from GET client requests $_REQUEST Combined data from POST and GET client requests

(derived from $_POST and $_GET)

; Accessing $_REQUEST is the equivalent in PHP to using the param routine in Perl

$_REQUEST[’username’] Value entered into field with name ‘username’ $_REQUEST[’fullname’] Value entered into field with name ‘fullname’

COMP284 Scripting Languages Lecture 12 Slide L12 – 8

Available information and Input Form data

Forms in PHP: Example (1)

• Create a web-based system that asks the user to enter the URL of a file containing bibliographic information

• Bibliographic informatiom will have the following form: @entry{

name={Jonas Lehner},

name={ Andreas Schoknecht},

title={You only live twice },

}

@entry{

name={ Andreas Schoknecht},

name={Eva Eggeling},

title={No End in Sight?},

}

• The system should extract the names, count them, and create a table of names and their frequency, ordered from most frequent to least frequent

COMP284 Scripting Languages Lecture 12 Slide L12 – 9

Available information and Input Form data

Forms in PHP: Example (1)

extract_names.php

The names occurring in
",htmlspecialchars($_REQUEST[’url’]),

"
are

$extracted_names\n";

} else {

echo <<

FORM;

}

?>

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/extract_names.php

COMP284 Scripting Languages Lecture 12 Slide L12 – 10

Available information and Input Form data

Forms in PHP: Example (1)

extraction.php

$number) {

$table .= "

}

$table = "

return $table;

} }

?> http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/extraction.php

COMP284 Scripting Languages Lecture 12 Slide L12 – 11

Available information and Input Form data

Web Applications Revisited

Select Item

Enter Address

Enter Payment

Confirm Order

App

App

App

App

App

Request

Resp onse

Request

Resp onse

Request

Resp onse

Request

Resp onse

Request

• An interaction between a user and a server-side web application often requires a sequence of requests and responses

• For each request, the application starts from scratch

• it does not maintain a state between consecutive requests

• it does not know whether the requests come from the same user or different users

; data needs to be transferred from one execution of the application to the next

COMP284 Scripting Languages Lecture 12 Slide L12 – 12

Available information and Input Form data

Transfer of Data: Example

• Assume for a sequence of requests we do not care whether they come from the same user or different users

• Then hidden inputs can be used for the transfer of data from one request / page to the next

form1.php

form2.php

process.php

COMP284 Scripting Languages Lecture 12 Slide L12 – 13

PHP sessions

Sessions

• By default, HTML and web servers do not keep track whether several client requests come from the same user or different users

Thus, a process that spans several pages, for example, placing an order, requires additional mechanisms

• Sessions help solve this problem by associating client requests with specific users and maintaining data during a user’s visit

• Sessions are often linked to user authentication but session can be used without user authentication, for example, eCommerce websites maintain a ‘shopping basket’ without requiring user authentication first

However, sessions are the mechanism that is typically used to allow or deny access to web pages based on a user having been authenticated

COMP284 Scripting Languages Lecture 12 Slide L12 – 14

PHP sessions

Sessions

• Servers keep track of a user’s sessions by using a session identifier, which

• is generated by the server when a session starts and • is then used by the browser when the user requests a page from the server

The session identifier can be sent through a cookie or by passing the session identifier in client requests

• In addition, one can use session variables for storing information to relate to a user and her session (session data), for example, the items of an order

• Sessions only store information temporarily If one needs to preserve information between visits by the same user, one needs to consider a method such as using a cookie or a database to store such information

COMP284 Scripting Languages Lecture 12 Slide L12 – 15

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/extract_names.php http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/extraction.php

PHP sessions

Cookies

Browser −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−→ Server GET /index.html HTTP/1.1

Host: intranet.csc.liv.ac.uk

Browser ←−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Server HTTP/1.0 200 OK

Content-type: text/html

Set-Cookie: name1=value1

Set-Cookie: name2=value2; Expires= Thu, 20 Mar 2014, 14:00 GMT

(content of index.html)

Browser −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−→ Server GET /teaching.html HTTP/1.1

Host: intranet.csc.liv.ac.uk

Cookie: name1=value1; name2=value2

Accept: */*

Browser ←−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Server HTTP/1.0 200 OK

Content-type: text/html

Set-Cookie: name1=value3

Set-Cookie: name2=value4; Expires= Fri, 21 Mar 2014, 14:00 GMT

Set-Cookie: name3=value5; Expires= Fri, 28 Mar 2014, 20:00 GMT

(content of teaching.html)

Wikipedia Contributors: HTTP Cookie. Wikipedia, The Free Encyclopedia, 5 March 2014 20:50. http://en.wikipedia.org/wiki/HTTP_cookie [accessed 6 Mar 2014]

COMP284 Scripting Languages Lecture 12 Slide L12 – 16

PHP sessions

PHP sessions

Sesssions proceed as follows

1 Start a PHP session – bool session_start() – string session_id([id]) – bool session_regenerate_id([delete_old])

2 Maintain session data – bool session_start() – $_SESSION array – bool isset($_SESSION[key]) – (interacting with a database)

3 End a PHP session – bool session_destroy() – void session_unset() – bool setcookie(name, value, expires, path)

COMP284 Scripting Languages Lecture 12 Slide L12 – 17

PHP sessions Start a PHP session

Start a session

• bool session_start() • creates a session • creates a session identifier (session id) when a session is created • sets up $_SESSION array that stores session variables and session data • the function must be executed before any other header calls

or output is produced

• string session_id([id]) • get or set the session id for the current session • the constant SID can also be used to retrieve the current name and

session id as a string suitable for adding to URLs

• string session_name([name]) • returns the name of the current session • if a name is given, the current session name will be replaced with the given

one and the old name returned

COMP284 Scripting Languages Lecture 12 Slide L12 – 18

PHP sessions Start a PHP session

Start a PHP session

• bool session_regenerate_id([delete_old]) • replaces the current session id with a new one • by default keeps the current session information stored in $_SESSION • if the optional boolean agument is TRUE, then the current session

information is deleted

; regular use of this function alleviates the risk of a session being ‘hijacked’

";

echo "Session name: ",session_name (),"
";

session_regenerate_id ();

echo "Session id: ",session_id (),"
"; // changed

echo "Session name: ",session_name (),"
"; // unchanged

?>

COMP284 Scripting Languages Lecture 12 Slide L12 – 19

PHP sessions Maintain session data

Maintain session data

• bool session_start()

• resumes the current session based on a session identifier passed via a GET or POST request, or passed via a cookie

• restores session variables and session data into $_SESSION

• the function must be executed before any other header calls or output is produced

• $_SESSION array • an associative array containing session variables and session data • you are responsible for choosing keys (session variables)

and maintaining the associated values (session data)

• bool isset($_SESSION[key]) returns TRUE iff $_SESSION[key] has already been assigned a value

COMP284 Scripting Languages Lecture 12 Slide L12 – 20

PHP sessions Maintain session data

Maintain session data

• bool session_start() • $_SESSION array • bool isset($_SESSION[key])

\n";

?>

COMP284 Scripting Languages Lecture 12 Slide L12 – 21

PHP sessions End a PHP session

End a PHP session

• bool session_destroy() • destroys all of the data associated with the current session • it does not unset any of the global variables associated with the session,

or unset the session cookie

• void session_unset() • frees all session variables currently registered

• bool setcookie(name, value, expires, path) • defines a cookie to be sent along with the rest of the HTTP headers • must be sent before any output from the script • the first argument is the name of the cookie • the second argument is the value of the cookie • the third argument is time the cookie expires (as a Unix timestamp), and • the fourth argument is the parth on the server in which the cookie will be

available

COMP284 Scripting Languages Lecture 12 Slide L12 – 22

PHP sessions End a PHP session

End a PHP session

• bool session_destroy() • destroys all of the data associated with the current session

• void session_unset() • frees all session variables currently registered

• bool setcookie(name, value, expires, path) • defines a cookie to be sent along with the rest of the HTTP headers

Note: Closing your web browser will also end a session COMP284 Scripting Languages Lecture 12 Slide L12 – 23

http://en.wikipedia.org/wiki/HTTP_cookie

PHP sessions Session management

More on session management

The following code tracks whether a session is active and ends the session if there has been no activity for more then 30 minutes if (isset($_SESSION[’LAST_ACTIVITY ’]) &&

(time() - $_SESSION[’LAST_ACTIVITY ’] > 1800)) {

// last request was more than 30 minates ago

session_destroy (); // destroy session data in storage

session_unset (); // unset session variables

if (session_id () != "" || isset($_COOKIE[session_name ()]))

setcookie(session_name (), session_id (),time () -2592000 ,’/’);

} else {

// update last activity time stamp

$_SESSION[’LAST_ACTIVITY ’] = time ();

}

The following code generates a new session identifier every 30 minutes

if (! isset($_SESSION[’CREATED ’])) {

$_SESSION[’CREATED ’] = time ();

} else if (time() - $_SESSION[’CREATED ’] > 1800) {

// session started more than 30 minates ago

session_regenerate_id(true);

$_SESSION[’CREATED ’] = time ();

}

http://stackoverflow.com/questions/520237/how-do-i-expire-a-php-session-after-30-minutes

COMP284 Scripting Languages Lecture 12 Slide L12 – 24

PHP sessions Example

PHP sessions: Example

mylibrary.php:

COMP284 Scripting Languages Lecture 12 Slide L12 – 25

PHP sessions Example

PHP sessions: Example

page1.php:

\n";

echo "Hello visitor!
This is your page request no ";

echo count_requests ()." from this site.
\n";

echo ’Continue |

Finish ’;

?>

finish.php:

\n";

echo "Goodbye visitor!
\n";

echo ’Start again ’;

?>

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/page1.php

COMP284 Scripting Languages Lecture 12 Slide L12 – 26

PHP sessions Example

PHP and Cookies

Cookies can survive a session and transfer information from one session to the next cmylibrary.php:

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/cpage1.php COMP284 Scripting Languages Lecture 12 Slide L12 – 27

Authentication Overview

PHP Sessions and Authentication

• Sessions are the mechanism that is typically used to allow or deny access to web pages based on a user having been authenticated

• Outline solution: • We want to protect a page content.php from unauthorised use • Before being allowed to access content.php, users must first authenticate

themselves by providing a username and password on the page login.php

• The system maintains a list of valid usernames and passwords in a database and checks usernames and passwords entered by the user against that database If the check succeeds, a session variable is set

• The page content.php checks whether this session variable is set If the session variable is set, the user will see the content of the page If the session variable is not set, the user is redirected to login.php

• The system also provides a logout.php page to allow the user to log out again

COMP284 Scripting Languages Lecture 12 Slide L12 – 28

Authentication Example

PHP Sessions and Authentication: Example

Second part of login.php:

Login

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/login.php COMP284 Scripting Languages Lecture 12 Slide L12 – 29

Authentication Example

PHP Sessions and Authentication: Example

First part of login.php:

COMP284 Scripting Languages Lecture 12 Slide L12 – 30

Authentication Example

PHP Sessions and Authentication: Example

content.php:

Protected Content

Welcome

Log Out

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/content.php

COMP284 Scripting Languages Lecture 12 Slide L12 – 31

http://stackoverflow.com/questions/520237/how-do-i-expire-a-php-session-after-30-minutes http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/page1.php http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/cpage1.php http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/login.php http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/content.php

Authentication Example

PHP Sessions and Authentication: Example

logout.php:

Logout

Goodbye

Login

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/logout.php

COMP284 Scripting Languages Lecture 12 Slide L12 – 32

Authentication Example

Revision

Read

• Chapter 10: Accessing MySQL Using PHP • Chapter 11: Form Handling • Chapter 13: Cookies, Sessions, and Authentication of

R. Nixon: Learning PHP, MySQL, and JavaScript. O’Reilly, 2009.

COMP284 Scripting Languages Lecture 12 Slide L12 – 33

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/logout.php

COMP284 Scripting Languages Lecture 13: PHP (Part 5)

Handouts (8 on 1)

Ullrich Hustadt

Department of Computer Science School of Electrical Engineering, Electronics, and Computer Science

University of Liverpool

Contents

31 Classes Defining and Instantiating a Class Visibility Class Constants Static Properties and Methods Destructors Inheritance Interfaces Introspection Functions

32 The PDO Class Introduction Connections Queries and Processing of Results Prepared Statements Transactions

COMP284 Scripting Languages Lecture 13 Slide L13 – 1

Classes Defining and Instantiating a Class

Defining and Instantiating a Class

• PHP is an object-oriented language with classes • A class can be defined as follows:

class identifier {

property_definitions

function_definitions

}

• The class name identifier is case-sensitive • The body of a class consists of property definitions and function definitions • The function definitions may include the definition of a constructor

• An object of a class is created using new identifier(arg1 ,arg2 ,...)

where arg1,arg2,... is a possibly empty list of arguments passed to the constructor of the class identifier

COMP284 Scripting Languages Lecture 13 Slide L13 – 2

Classes Defining and Instantiating a Class

A Closer Look at Class Definitions

In more detail, the definition of a class typically looks as follows class identifier {

# Properties

vis $attrib1

...

vis $attribN = value

# Constructor

function __construct(p1 ,...) {

statements

}

# Methods

vis function method1(p1 ,...) {

statements

}

vis function methodN(p1 ,...) {

statements

}

}

• Every instance obj of this class will have attributes attrib1,. . . and methods method1(), . . . accessible as obj->attrib1 and obj->method1(a1...)

• __construct is the constructor of the class and will be called whenever new identifier(a1,...)

is executed

• vis is a declaration of the visibility of each attribute and method

COMP284 Scripting Languages Lecture 13 Slide L13 – 3

Classes Defining and Instantiating a Class

A Closer Look at Class Definitions

• The pseudo-variable $this is available when a method is called from within an object context and is a reference to the calling object

• Inside method definitions, $this can be used to refer to the properties and methods of the calling object

• The object operator -> is used to access methods and properties of the calling object

class Rectangle {

protected $height;

protected $width;

function __construct($height ,$width) {

$this ->width = $width;

$this ->height = $height;

}

}

COMP284 Scripting Languages Lecture 13 Slide L13 – 4

Classes Visibility

Visibility

• Properties and methods can be declared as public accessible everywhere private accessible only within the same class protected accessible only within the class itself and

by inheriting and parent classes

• For properties, a visibility declaration is required

• For methods, a visibility declaration is optional ; by default, methods

are public

• Accessing a private or protected property / method outside its visibility is a fatal error

class Vis {

public $public = 1;

private $private = 2;

protected $protected = 3;

protected function proFc() {}

private function priFc() {}

}

$v = new Vis ();

echo $v->public; # prints 1

echo $v->private; # Fatal Error

echo $v->protected; # Fatal Error

echo $v->priFc (); # Fatal Error

echo $v->proFc (); # Fatal Error

COMP284 Scripting Languages Lecture 13 Slide L13 – 5

Classes Class Constants

Constants

• Classes can have their own constants and constants can be declared to be public, private or protected ; by default, class constants are public vis const identifier = value;

• Accessing a private or protected constant outside its visibility is a fatal error ; execution of the script stops

• Class constants are allocated once per class, and not for each class instance

• Class constants are accessed using the scope resolution operator ::

class MyClass {

const SIZE = 10;

}

echo MyClass ::SIZE; # prints 10

$o = new MyClass ();

echo $o::SIZE; # prints 10

COMP284 Scripting Languages Lecture 13 Slide L13 – 6

Classes Static Properties and Methods

Static Properties and Methods

• Class properties or methods can be declared static • Static class properties and methods are accessed (via the class) using

the scope resolution operator ::

• Static class properties cannot be accessed via an instantiated class object, but static class methods can

• Static class method have no access to $this

class Employee {

static $totalNumber = 0;

public $name;

function __construct($name) {

$this ->$name = $name;

Employee :: $totalNumber ++;

} }

$e1 = new Employee("Ada");

$e2 = new Employee("Ben");

echo Employee :: $totalNumber # prints 2

COMP284 Scripting Languages Lecture 13 Slide L13 – 7

Classes Destructors

Destructors

• A class can have a destructor method __destruct that will be called as soon as there are no other references to a particular object

class Employee {

static $totalNumber = 0;

public $name;

function __construct($name) {

$this ->name = $name;

Employee :: $totalNumber ++;

}

function __destruct () {

Employee :: $totalNumber --;

}

}

$e1 = new Employee("Ada");

$e2 = new Employee("Ben");

echo Employee :: $totalNumber # prints 2

$e1 = null;

echo Employee :: $totalNumber # prints 1

COMP284 Scripting Languages Lecture 13 Slide L13 – 8

Classes Inheritance

Inheritance

• In a class definition it is possible to specify one parent class from which a class inherits constants, properties and methods:

class identifier1 extends identifier2 { ... }

• The constructor of the parent class is not automatically called it must be called explicitly from the child class

• Inherited constants, properties and methods can be overridden by redeclaring them with the same name defined in the parent class

• The declaration final can be used to prevent a method from being overriden

• Using parent:: it is possible to access overridden methods or static properties of the parent class

• Using self:: it is possible to access static properties and methods of the current class

COMP284 Scripting Languages Lecture 13 Slide L13 – 9

Classes Inheritance

Inheritance: Example

class Rectangle {

protected $height;

protected $width;

function __construct($height ,$width) {

$this ->width = $width;

$this ->height = $height;

}

function area() {

return $this ->width * $this ->height;

} }

class Square extends Rectangle {

function __construct($size) {

parent :: __construct($size ,$size);

} }

$rt1 = new Rectangle (3,4);

echo "\$rt1 area = ",$rt1 ->area(),"\n";

$sq1 = new Square (5);

echo "\$sq1 area = ",$sq1 ->area(),"\n";

$rt1 area = 12

$sq1 area = 15

COMP284 Scripting Languages Lecture 13 Slide L13 – 10

Classes Interfaces

Interfaces

• Interfaces specify which methods a class must implement without providing an implementation

• Interfaces are defined in the same way as a class with the keyword class replaced by interface

• All methods in an interface must be declared public • A class can declare that it implements one ore more interfaces using the implements keyword

interface Shape {

public function area ();

}

class Rectangle implements Shape {

...

}

COMP284 Scripting Languages Lecture 13 Slide L13 – 11

Classes Introspection Functions

Introspection Functions

There are functions for inspecting objects and classes:

bool class_exists(string class)

returns TRUE iff a class class exists class_exists(’Rectangle’) # returns TRUE

string get_class(object obj)

returns the name of the class to which an object belongs get_class($sq1) # returns ’Square’

bool is_a(object obj, string class)

returns TRUE iff obj is an instance of class named class is_a($sq1,’Rectangle’) # returns TRUE

bool method_exists(object obj,string method)

returns TRUE iff obj has a method named method method_exists($sq1,’area’) # returns TRUE

COMP284 Scripting Languages Lecture 13 Slide L13 – 12

Classes Introspection Functions

Introspection Functions

There are functions for inspecting objects and classes:

bool property_exists(object obj,string property)

returns TRUE iff object has a property named property

property_exists($sq1,’size’) # returns FALSE

get_object_vars(object)

returns an array with the accessible non-static properties of object

mapped to their values get_object_vars($e2)

# returns ["name" => "Ben"]

get_class_methods(class)

returns an array of method names defined for class get_class_methods(’Square’)

# returns ["__construct", "area"]

COMP284 Scripting Languages Lecture 13 Slide L13 – 13

The PDO Class Introduction

The PDO Class

• The PHP Data Objects (PDO) extension defines an interface for accessing databases in PHP

• Various PDO drivers implement that interface for specific database management systems

• PDO_MYSQL implements the PDO interface for MySQL 3.x to 5.x • PDO_SQLSRV implements the PDO interface for MS SQL Server and SQL

Azure

COMP284 Scripting Languages Lecture 13 Slide L13 – 14

The PDO Class Connections

Connections

• Before we can interact with a DBMS we need to establish a connection to it

• A connection is established by creating an instance of the PDO class • The constructor for the PDO class accepts arguments that specify the

database source (DSN), username, password and additional options

$pdo = new PDO(dsn ,username ,password ,options );

• Upon successful connection to the database, the constructor returns an instance of the PDO class

• The connection remains active for the lifetime of that PDO object • Assigning NULL to the variable storing the PDO object destroys it and

closes the connection

$pdo = NULL

COMP284 Scripting Languages Lecture 13 Slide L13 – 15

The PDO Class Connections

Connections: Example

# Connection information for the Departmental MySQL Server

$host = "mysql";

$user = "ullrich";

$passwd = "-------";

$db = "ullrich";

$charset = "utf8mb4";

$dsn = "mysql:host=$host;dbname=$db;charset=$charset";

# Useful options

$opt = array(

PDO:: ATTR_ERRMODE => PDO:: ERRMODE_EXCEPTION ,

PDO:: ATTR_DEFAULT_FETCH_MODE => PDO:: FETCH_ASSOC ,

PDO:: ATTR_EMULATE_PREPARES => false

);

try {

$pdo = new PDO($dsn ,$user ,$passwd ,$opt);

} catch (PDOException $e) {

echo ’Connection failed: ’,$e->getMessage ();

}

COMP284 Scripting Languages Lecture 13 Slide L13 – 16

The PDO Class Queries and Processing of Results

Queries

• The query() method of PDO objects can be used to execute an SQL query

$result = $pdo->query(statement)

$result = $pdo->query("SELECT * FROM meetings")

• query() returns the result set (if any) of the SQL query as a PDOStatement object

• The exec() method of PDO objects executes an SQL statement, returning the number of rows affected by the statement

$rowNum = $pdo->exec(statement)

$rowNum = $pdo->exec("DELETE * FROM meetings")

COMP284 Scripting Languages Lecture 13 Slide L13 – 17

The PDO Class Queries and Processing of Results

Processing Result Sets

• To get a single row as an array from a result set stored in a PDOStatement object, we can use the fetch() method

• By default, PDO returns each row as an array indexed by the column name and 0-indexed column position in the row

$row = $result ->fetch ()

array(’slot’ => 1,

’name’ => ’Michael North ’,

’email’ => ’M.North@student.liverpool.ac.uk’,

0 => 1,

1 => ’Michael North’,

2 => ’M.North@student.liverpool.ac.uk’)

• After the last call of fetch() the result set should be released using $rows = $result ->closeCursor ()

• The get all rows as an array of arrays from a result set stored in a PDOStatement object, we can use the fetchAll() method $rows = $result ->fetchAll ()

COMP284 Scripting Languages Lecture 13 Slide L13 – 18

The PDO Class Queries and Processing of Results

Processing Result Sets

• We can use a while-loop together with the fetch() method to iterate over all rows in a result set

while ($row = $result ->fetch ()) {

echo "Slot: ",$row["slot"], "
\n";

echo "Name: ",$row["name"], "
\n";

echo "Email: ",$row["email"],"

\n";

}

• Alternatively, we can use a foreach-loop foreach($result as $row) {

echo "Slot: ",$row["slot"], "
\n";

echo "Name: ",$row["name"], "
\n";

echo "Email: ",$row["email"],"

\n";

}

COMP284 Scripting Languages Lecture 13 Slide L13 – 19

The PDO Class Queries and Processing of Results

Processing Result Sets

• Using bindColumn() we can bind a variable a particular column in the result set from a query

• columns can be specified by number (starting with 1!) • columns can be specified by name (matching case)

• Each call to fetch() and fetchAll() will then update all the variables that are bound to columns

• The binding needs to be renewed after each query execution

$result ->bindColumn (1, $slot); # bind by column no

$result ->bindColumn (2, $name);

$result ->bindColumn(’email’, $email ); # bind by column name

while ($row = $result ->fetch(PDO:: FETCH_BOUND )) {

echo "Slot: ",$slot , "
\n";

echo "Name: ",$name , "
\n";

echo "Email: ",$email ,"

\n";

}

COMP284 Scripting Languages Lecture 13 Slide L13 – 20

The PDO Class Prepared Statements

Prepared Statements

• The use of parameterised prepared statements is preferable over queries • Prepared statements are are parsed, analysed, compiled and optimised

only once

• Prepared statements can be executed repeatedly with different arguments

• Arguments to prepared statements do not need to be quoted and binding of parameters to arguments will automatically prevent SQL injection

• PDO can emulate prepared statements for a DBMS that does not support them

• MySQL supports prepared statements natively, so PDO emulation should be turned off

$pdo ->setAttribute(PDO:: ATTR_EMULATE_PREPARES , FALSE );

COMP284 Scripting Languages Lecture 13 Slide L13 – 21

The PDO Class Prepared Statements

Prepared Statements: SQL Templates

• An SQL template is an SQL query (as a string) possibily containing either

• named parameters of the form :name, where name is a PHP identifier, or • question marks ? for which values will be substituted when the query is executed

$tpl1 = "select slot from meetings where

name=:name and email =:email";

$tpl2 = "select slot from meetings where name=?";

• The PDO method prepare() turns an SQL template into prepared statement (by asking the DBMS to do so)

• on success, a PDOStatement object is returned • on failure, FALSE or an error will be returned

$stmt1 = $pdo ->prepare($tpl1 );

$stmt2 = $pdo ->prepare("select * from fruit where col=?");

COMP284 Scripting Languages Lecture 13 Slide L13 – 22

The PDO Class Prepared Statements

Prepared Statements: Binding

• We can bind the parameters of a PDOStatement object to a value using the bindValue() method

• Named parameters are bound by name • Question mark parameters are bound by position (starting from 1!) • the datatype of the value can optionally be declared

(to match that of the corresponding database field)

• the value is bound to the parameter at the time bindValue() is executed

$stmt1 ->bindValue(’:name’,’Ben’,PDO:: PARAM_STR );

$email = ’bj1@liv.ac.uk’;

$stmt1 ->bindValue(’:email’,$email );

$stmt2 ->bindValue (1,20,PDO:: PARAM_INT );

COMP284 Scripting Languages Lecture 13 Slide L13 – 23

The PDO Class Prepared Statements

Prepared Statements: Binding

• We can bind the parameters of a PDOStatement object to a variable using the bindParam() method

• Named parameters are bound by name • Question mark parameters are bound by position (starting from 1!) • the datatype of the value can optionally be declared

(to match that of the corresponding database field)

• the variable is bound to the parameter as a reference • a value is only substituted when the statement is executed

$name = ’Ben’;

$stmt1 ->bindParam(’:name’,$name ,PDO:: PARAM_STR );

$stmt1 ->bindParam(’:email’,$email );

$email = ’bj1@liv.ac.uk’;

$slot = 20;

$stmt2 ->bindParam(1,$slot ,PDO:: PARAM_INT );

• It is possible to mix bindParam() and bindValue()

COMP284 Scripting Languages Lecture 13 Slide L13 – 24

The PDO Class Prepared Statements

Prepared Statements: Execution

• Prepared statements are executed using execute() method • Parameters must • previously have been bound using bindValue() or bindParam(), or • be given as an array of values to execute

; take precedence over previous bindings ; are bound using bindValue()

• execute() returns TRUE on success or FALSE on failure • On success, the PDOStatement object stores a result set (if appropriate)

$stmt1 ->execute ();

$stmt1 ->execute(array(’:name’ => ’Eve’, ’:email’ => $email ));

$stmt2 ->execute(array (10));

COMP284 Scripting Languages Lecture 13 Slide L13 – 25

The PDO Class Transactions

Transactions

• There are often situations where a single ‘unit of work’ requires a sequence of database operations ; e.g., bookings, transfers

• By default, PDO runs in ”auto-commit” mode ; successfully executed SQL statements cannot be ‘undone’

• To execute a sequence of SQL statements whose changes are • only committed at the end once all have been successful or • rolled back otherwise, PDO provides the methods

• beginTransaction() • commit() • rollBack()

COMP284 Scripting Languages Lecture 13 Slide L13 – 26

The PDO Class Transactions

Transactions

To support transactions, PDO provides the methods beginTransaction()

– turns off auto-commit mode; changes to the database are not committed until commit() is called

– returns TRUE on success or FALSE on failure – throws an exception if another transaction is already active

commit()

– changes to the database are made permanent; auto-commit mode is turned on

– returns TRUE on success or FALSE on failure – throws an exception if no transaction is active

rollBack()

– discard changes to the database; auto-commit mode is restored – returns TRUE on success or FALSE on failure – throws an exception if no transaction is active

COMP284 Scripting Languages Lecture 13 Slide L13 – 27

The PDO Class Transactions

Transactions: Example $pdo = new PDO(’mysql:host =...; dbname =...’,’...’,’...’,

array(PDO:: ATTR_ERRMODE => PDO:: ERRMODE_EXCEPTION ,

PDO:: ATTR_EMULATE_PREPARES => false ));

$pdo ->beginTransaction ();

try{

$userId = 1; $paymentAmount = 10.50;

// Query 1: Attempt to insert a payment record

$sql = "INSERT INTO payments (user_id , amount) VALUES (?, ?)";

$stmt = $pdo ->prepare($sql);

$stmt ->execute(array($userId ,$paymentAmount ));

// Query 2: Attempt to update the user’s account

$sql = "UPDATE accounts SET balance = balance + ? WHERE id = ?";

$stmt = $pdo ->prepare($sql);

$stmt ->execute(array($paymentAmount ,$userId ));

// Commit the transaction

$pdo ->commit ();

} catch(Exception $e){

echo $e->getMessage ();

// Rollback the transaction

$pdo ->rollBack ();

} Based on http://thisinterestsme.com/php-pdo-transaction-example/

COMP284 Scripting Languages Lecture 13 Slide L13 – 28

The PDO Class Transactions

Revision

Read

• Language Reference: Classes and Objects http://php.net/manual/en/language.oop5.php

• The PDO Class http://php.net/manual/en/class.pdo.php

of M. Achour, F. Betz, A. Dovgal, et al: PHP Manual. The PHP Group, 2017. http://uk.php.net/manual/en [accessed 07 Dec 2017]

COMP284 Scripting Languages Lecture 13 Slide L13 – 29

PHP: PDO transaction example.

http://php.net/manual/en/language.oop5.php http://php.net/manual/en/class.pdo.php http://uk.php.net/manual/en

COMP284 Scripting Languages Lecture 14: JavaScript (Part 1)

Handouts (8 on 1)

Ullrich Hustadt

Department of Computer Science School of Electrical Engineering, Electronics, and Computer Science

University of Liverpool

Contents

33 JavaScript Motivation Overview Example

34 Types and Variables Types Variables Typecasting Comparisons

COMP284 Scripting Languages Lecture 14 Slide L14 – 1

JavaScript Motivation

JavaScript: Motivation

• PHP and Perl both allow us to create dynamic web pages • In web applications, PHP and Perl code is executed on the web server

(server-side scripting)

• allows to use a website template that is instantiated using data stored in a database

• ‘business logic’ is hidden from the user: the code of an application is not visible to the user/client; the user/client only has access to the HTML produced by the code

• not ideal for interactive web applications: too slow to react and too much data needs to be transferred

• operations that refer to the location of the user/client are difficult, for example, displaying the local time

echo date(’H:i l, j F Y’);

displays the local time on the server not the local time for the user

COMP284 Scripting Languages Lecture 14 Slide L14 – 2

JavaScript Overview

JavaScript

• JavaScript is a language for client-side scripting • script code is embedded in a web page (as for PHP),

but delivered to the client as part of the web page and executed by the user’s web browser ; code is visible to the user/client

• allows for better interactivity as reaction time is improved and data exchange with the server can be minimised

• a web browser may not support JavaScript or the user may have disallowed the execution of JavaScript code

• different JavaScript engines may lead to different results, in particular, results not anticipated by the developer of JavaScript code

• performance relies on the efficiency of the JavaScript engine and the client’s computing power (not the server’s)

• operations that refer to the location of the client are easy:

document.write("Local time: " + (new Date). toString ());

COMP284 Scripting Languages Lecture 14 Slide L14 – 3

JavaScript Overview

JavaScript: History

• originally developed by Brendan Eich at Netscape under the name Mocha

• first shipped together with Netscape browser in September 1995 under the name LiveScript

• obtained its current name in December 1995 under a deal between Netscape and Sun Microsystems, the company behind Java, in December 1995

• does not have a particularly close relationship to Java, it mixes aspects of Java with aspects of PHP and Perl and its own peculiarities

• is a dialect of ECMAScript, a scripting language standardised in the ECMA-262 specification and ISO/IEC 16262 standard since June 1997

• other dialects include Microsoft’s JScript and TypeScript and Adobe’s ActionScript

COMP284 Scripting Languages Lecture 14 Slide L14 – 4

JavaScript Overview

Websites and Programming Languages

Website Client-Side Server-Side Database

Google JavaScript C, C++, Go, Java, Python, PHP

BigTable, MariaDB

Facebook JavaScript Hack, PHP, Python, C++, Java, . . .

MariaDB, MySQL, HBase Cassandra

YouTube Flash, JavaScript

C, C++, Python, Java, Go

BigTable, MariaDB

Yahoo JavaScript PHP MySQL, PostgreSQL

Amazon JavaScript Java, C++, Perl Oracle Database

Wikipedia JavaScript PHP, Hack MySQL, MariaDB

Twitter JavaScript C++, Java, Scala MySQL

Bing JavaScript ASP.NET MS SQL Server Wikipedia Contributors: Programming languages used in most popular websites. Wikipedia, The Free Encyclopedia, 20 October 2017, at 11:28. http://en.wikipedia.org/wiki/Programming_languages_used_in_most_popular_websites [accessed 23 October 2017]

COMP284 Scripting Languages Lecture 14 Slide L14 – 5

JavaScript Example

JavaScript: Hello World!

1 2 3

Our first JavaScript script

4 7

10

• JavaScript code is enclosed between
• Alternative HTML markup that is to be used in case JavaScript is not

enabled or supported by the web browser, can be specified 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

• No particular file name extension is required

COMP284 Scripting Languages Lecture 14 Slide L14 – 6

JavaScript Example

JavaScript scripts

• JavaScript scripts are embedded into HTML documents and are
enclosed between

where url is the (relative or absolute) URL for library

• One such import statement is required for each library
• Import statements are typically placed in the head section of a page or

at the end of the body section

• Web browers typically cache libraries

COMP284 Scripting Languages Lecture 16 Slide L16 – 11

JavaScript libraries

JavaScript libraries: Example

~ullrich/public_html/sort.js

function bubble_sort(array) {

... swap(array , j, j+1) ...

return array

}

function swap(array , i, j) { ... }

example.html

COMP284 Scripting Languages Lecture 16 Slide L16 – 12

(User-defined) Objects Object Literals

Object Literals

• JavaScript is an object-oriented language, but one without classes

• Instead of defining a class,
we can simply state an object literal

{ property1: value1 , property2: value2 , ... }

where property1, property2, . . . are variable names
and value1, value2, . . . are values (expressions)

var person1 = {

age: (30 + 2),

gender: ’male’,

name: { first : ’Bob’, last : ’Smith’ },

interests: [’music ’, ’skiing ’],

hello: function () { return ’Hi! I\’m ’ + this.name.first + ’.’ }

};

person1.age --> 32 // dot notation

person1[’gender ’] --> ’male’ // bracket notation

person1.name.first --> ’Bob’

person1[’name’][’last’] --> ’Smith’

COMP284 Scripting Languages Lecture 16 Slide L16 – 13

(User-defined) Objects Object Literals

Object Literals

var person1 = {

...

name: { first : ’Bob’, last : ’Smith’ },

hello: function () { return ’Hi! I\’m ’ + this.name.first + ’.’ }

};

person1.hello() --> "Hi! I’m Bob."

• Every part of a JavaScript program is executed in a particular
execution context

• Every execution context offers a keyword this as a way of referring to
itself

• In person1.hello() the execution context of hello() is person1
; this.name.first is person1.name.first

COMP284 Scripting Languages Lecture 16 Slide L16 – 14

(User-defined) Objects Object Literals

Object Literals

var person1 = {

name: { first : ’Bob’, last : ’Smith’ },

greet: function () { return ’Hi! I\’m ’ + name.first + ’.’ },

full1: this.name.first + " " +this.name.last ,

full2: name.first + " " + name.last

};

person1.greet() --> "Hi! I’m undefined."

person1.full1 --> "undefined undefined"

person1.full2 --> "undefined undefined"

• In person1.greet() the execution context of greet() is person1
; but name.first does not refer to person1.name.first

• In the (construction of the) object literal itself, this does not refer to
person1 but its execution context (the window object)
; none of name.first, name.last, this.name.first, and

this.name.last refers to properties of this object literal

COMP284 Scripting Languages Lecture 16 Slide L16 – 15

(User-defined) Objects Object Constructors

Objects Constructors

• JavaScript is an object-oriented language, but one without classes

• Instead of defining a class,
we can define a function that acts as object constructor

• variables declared inside the function will be instance variables of the object
; each object will have its own copy of these variables

• it is possible to make such variables private or public
• inner functions will be methods of the object
• it is possible to make such functions/methods private or public
• private variables/methods can only be accessed inside the function
• public variables/methods can be accessed outside the function

• Whenever an object constructor is called,
prefixed with the keyword new, then

• a new object is created
• the function is executed with the keyword this bound to that object

COMP284 Scripting Languages Lecture 16 Slide L16 – 16

(User-defined) Objects Definition and use

Objects: Definition and use

function SomeObj () {

instVar2 = ’B’ // private variable

var instVar3 = ’C’ // private variable

this.instVar1 = ’A’ // public variable

this.method1 = function () { // public method

// use of a public variable , e.g. ‘instVar1 ’, must be preceded by ‘this’

return ’m1[’ + this.instVar1 + ’]’ + method3 () }

this.method2 = function () { // public method

// calls of a public method , e.g. ‘method1 ’, must be preceded by ‘this’

return ’ m2[’ + this.method1 () + ’]’ }

method3 = function () { // private method

return ’ m3[’ + instVar2 + ’]’ + method4 () }

var method4 = function () { // private method

return ’ m4[’ + instVar3 + ’]’ }

}

obj = new SomeObj () // creates a new object

obj.instVar1 --> "A"

obj.instVar2 --> undefined

obj.instVar3 --> undefined

obj.method1 () --> "m1[A] m3[B] m4[C]"

obj.method2 () --> "m2[m1[A] m3[B] m4[C]]"

obj.method3 () --> error

obj.method4 () --> error

COMP284 Scripting Languages Lecture 16 Slide L16 – 17

(User-defined) Objects Definition and use

Objects: Definition and use

function SomeObj () {

this.instVar1 = ’A’ // public variable

instVar2 = ’B’ // private variable

var instVar3 = ’C’ // private variable

this.method1 = function () { ... } // public method

this.method2 = function () { ... } // public method

method3 = function () { ... } // private method

var method4 = function () { ... } // private method

}

• Note that all of instVar1 to instVar3, method1 to method4 are
instance variables (properties, members) of someObj

• The only difference is that instVar1 to instVar3 store strings while
method1 to method4 store functions

; every object stores its own copy of the methods

COMP284 Scripting Languages Lecture 16 Slide L16 – 18

(User-defined) Objects Prototype property

Objects: Prototype property

• All functions have a prototype property that can hold
shared object properties and methods
; objects do not store their own copies of these properties and

methods but only store references to a single copy

function SomeObj () {

this.instVar1 = ’A’ // public variable

instVar2 = ’B’ // private variable

var instVar3 = ’C’ // private variable

SomeObj.prototype.method1 = function () { ... } // public

SomeObj.prototype.method2 = function () { ... } // public

method3 = function () { ... } // private method

var method4 = function () { ... } // private method

}

Note: prototype properties and methods are always public!

COMP284 Scripting Languages Lecture 16 Slide L16 – 19

(User-defined) Objects Prototype property

Objects: Prototype property

• The prototype property can be modified ‘on-the-fly’
; all already existing objects gain new properties / methods
; manipulation of properties / methods associated with the

prototype property needs to be done with care

function SomeObj () { ... }

obj1 = new SomeObj ()

obj2 = new SomeObj ()

document.writeln(obj1.instVar4) // undefined

document.writeln(obj2.instVar4) // undefined

SomeObj.prototype.instVar4 = ’A’

document.writeln(obj1.instVar4) // ’A’

document.writeln(obj2.instVar4) // ’A’

SomeObj.prototype.instVar4 = ’B’

document.writeln(obj1.instVar4) // ’B’

document.writeln(obj2.instVar4) // ’B’

obj1.instVar4 = ’C’ // creates a new instance variable for obj1

SomeObj.prototype.instVar4 = ’D’

document.writeln(obj1.instVar4) // ’C’ !!

document.writeln(obj2.instVar4) // ’D’ !!
COMP284 Scripting Languages Lecture 16 Slide L16 – 20

(User-defined) Objects Prototype property

Objects: Prototype property

• The prototype property can be modified ‘on-the-fly’
; all already existing objects gain new properties / methods
; manipulation of properties / methods associated with the

prototype property needs to be done with care

function SomeObj () { ... }

obj1 = new SomeObj ()

obj2 = new SomeObj ()

SomeObj.prototype.instVar5 = ’E’

SomeObj.prototype.setInstVar5 = function(arg) {

this.instVar5 = arg

}

obj1.setInstVar5(’E’)

obj2.setInstVar5(’F’)

document.writeln(obj1.instVar5) // ’E’ !!

document.writeln(obj2.instVar5) // ’F’ !!

COMP284 Scripting Languages Lecture 16 Slide L16 – 21

(User-defined) Objects Public and private static variables

‘Class’ variables and ‘Class’ methods

Function properties can be used to emulate Java’s class variables
(static variables shared among instances) and class methods
function Circle(radius) { this.r = radius }

// ‘class variable ’ - property of the Circle constructor function

Circle.PI = 3.14159

// ‘instance method ’

Circle.prototype.area = function () {

return Circle.PI * this.r * this.r; }

// ‘class method ’ - property of the Circle constructor function

Circle.max = function (cx ,cy) {

if (cx.r > cy.r) { return cx } else { return cy }

}

c1 = new Circle (1.0) // create an instance of the Circle class

c1.r = 2.2; // set the r instance variable

c1_area = c1.area (); // invoke the area() instance method

x = Math.exp(Circle.PI) // use the PI class variable in a computation

c2 = new Circle (1.2) // create another Circle instance

bigger = Circle.max(c1 ,c2) // use the max() class method

COMP284 Scripting Languages Lecture 16 Slide L16 – 22

(User-defined) Objects Public and private static variables

Private static variables

In order to create private static variables shared between objects
we can use a self-executing anonymous function
var Person = (function () {

var population = 0 // private static ‘class’ variable

return function (value) { // constructor

population ++

var name = value // private instance variable

this.setName = function (value) { name = value }

this.getName = function () { return name }

this.getPop = function () { return population }

}

}())

person1 = new Person(’Peter’)

person2 = new Person(’James’)

person1.getName () --> ’Peter’

person2.getName () --> ’James’

person1.name --> undefined

Person.population || person1.population --> undefined

person1.getPop () --> 2

person1.setName(’David’)

person1.getName () --> ’David’

COMP284 Scripting Languages Lecture 16 Slide L16 – 23

(User-defined) Objects Pre-defined objects

Pre-defined objects: String

• JavaScript has a collection of pre-defined objects,
including Array, String, Date

• A String object encapsulates values of the primitive datatype string
• Properties of a String object include
• length the number of characters in the string

• Methods of a String object include
• charAt(index)

the character at position index (counting from 0)

• substring(start,end)
returns the part of a string between positions start (inclusive)
and end (exclusive)

• toUpperCase()
returns a copy of a string with all letters in uppercase

• toLowerCase()
returns a copy of a string with all letters in lowercase

COMP284 Scripting Languages Lecture 16 Slide L16 – 24

(User-defined) Objects Pre-defined objects

Pre-defined objects: String and RegExp

• JavaScript supports (Perl-like) regular expressions and the String objects
have methods that use regular expressions:

• search(regexp)
matches regexp with a string and returns the start position of the first
match if found, -1 if not

• match(regexp)
– without g modifier returns the matching groups for the first match

or if no match is found returns null
– with g modifier returns an array containing all the matches for

the whole expression

• replace(regexp,replacement)
replaces matches for regexp with replacement,
and returns the resulting string

name1 = ’Dave Shield ’.replace (/(\w+)\s(\w+)/, "$2 , $1")

regexp = new RegExp("(\\w+)\\s(\\w+)")

name2 = ’Ken Chan’.replace(regexp , "$2 , $1")

COMP284 Scripting Languages Lecture 16 Slide L16 – 25

(User-defined) Objects Pre-defined objects

Pre-defined objects: Date

• The Date object can be used to access the (local) date and time

• The Date object supports various constructors
• new Date() current date and time
• new Date(milliseconds) set date to milliseconds since 1 Januar 1970
• new Date(dateString) set date according to dateString
• new Date(year, month, day, hours, min, sec, msec)

• Methods provided by Date include
• toString()

returns a string representation of the Date object

• getFullYear()
returns a four digit string representation of the (current) year

• parse()
parses a date string and returns the number of milliseconds
since midnight of 1 January 1970

COMP284 Scripting Languages Lecture 16 Slide L16 – 26

(User-defined) Objects Pre-defined objects

Revision

Read

• Chapter 16: JavaScript Functions, Objects, and Arrays
• Chapter 17: JavaScript and PHP Validation and Error Handling

(Regular Expressions)
of

R. Nixon:
Learning PHP, MySQL, and JavaScript.
O’Reilly, 2009.

• http://coffeeonthekeyboard.com/
private-variables-in-javascript-177/

• http://coffeeonthekeyboard.com/
javascript-private-static-members-part-1-208/

• http://coffeeonthekeyboard.com/
javascript-private-static-members-part-2-218/

COMP284 Scripting Languages Lecture 16 Slide L16 – 27

http://coffeeonthekeyboard.com/private-variables-in-javascript-177/
http://coffeeonthekeyboard.com/private-variables-in-javascript-177/
http://coffeeonthekeyboard.com/javascript-private-static-members-part-1-208/
http://coffeeonthekeyboard.com/javascript-private-static-members-part-1-208/
http://coffeeonthekeyboard.com/javascript-private-static-members-part-2-218/
http://coffeeonthekeyboard.com/javascript-private-static-members-part-2-218/

COMP284 Scripting Languages
Lecture 17: JavaScript (Part 4)

Handouts (8 on 1)

Ullrich Hustadt

Department of Computer Science
School of Electrical Engineering, Electronics, and Computer Science

University of Liverpool

Contents

41 Dynamic web pages using JavaScript
Window and Document objects
Window object: Properties and methods
Dialog boxes
Input validation
Document object and Document Object Model

42 Event-driven Programs
Introduction

COMP284 Scripting Languages Lecture 17 Slide L17 – 1

Dynamic web pages using JavaScript Window and Document objects

Window and Document objects

JavaScript provides two objects that are essential to the creation of
dynamic web pages and interactive web applications:

window object

• a JavaScript object that represents a browser window or tab
• automatically created whith every instance of a or
tag

• allows properties of a window to be accessed and manipulated
; JavaScript provides methods that allow window objects to be

created and manipulated
Example: window.open(’http://www.csc.liv.ac.uk’,’Home’)

• whenever an object method or property is referenced in a script without
an object name and dot prefix it is assumed by JavaScript to be a
member of the window object

Example: We can write alert() instead of window.alert()

COMP284 Scripting Languages Lecture 17 Slide L17 – 2

Dynamic web pages using JavaScript Window object: Properties and methods

Window object

• A window object represents an open window in a browser.
• If a document contain frames, then there is
• one window object, window, for the HTML document
• and one additional window object for each frame,

accessible via an array window.frames

• A window object has properties including

document document object for the window

history history object for the window

location location object (current URL) for the window

navigator navigator (web browser) object for the window

opener reference to the window that created the window

innerHeight inner height of a window’s content area

innerWidth inner width of a window’s content area

closed boolean value indicating whether the window is
(still) open

COMP284 Scripting Languages Lecture 17 Slide L17 – 3

Dynamic web pages using JavaScript Window object: Properties and methods

Navigator object

Properties of a navigator object include

navigator.appName the web brower’s name

navigator.appVersion the web brower’s version

Example: Load different style sheets depending on browser

COMP284 Scripting Languages Lecture 17 Slide L17 – 4

Dynamic web pages using JavaScript Window object: Properties and methods

Window object

Methods provided by a window object include

• open(url, name [, features])
• opens a new browser window/tab
• returns a reference to a window object
• url is the URL to access in the new window; can be the empty string
• name is a name given to the window for later reference
• features is a string that determines various window features

The standard sequence for the creation of a new windows is not:

// new instance of ‘Window ’ class

var newWin = new Window (...)

newWin.document.write(’...’)

instead it is

// new window created by using ‘open’ with an existing one

var newWin = window.open (...)

newWin.document.write(’...’)

COMP284 Scripting Languages Lecture 17 Slide L17 – 5

Dynamic web pages using JavaScript Window object: Properties and methods

Window object

Methods provided by a window object include

• close()
• closes a browser window/tab

• focus()
• give focus to a window (bring the window to the front)

• blur()
• removes focus from a window (moves the window behind others)

• print()
• prints (sends to a printer) the contents of the current window

COMP284 Scripting Languages Lecture 17 Slide L17 – 6

Dynamic web pages using JavaScript Window object: Properties and methods

Window object: Example

COMP284 Scripting Languages Lecture 17 Slide L17 – 7

Dynamic web pages using JavaScript Dialog boxes

Window object: Dialog boxes

• Often we only want to open a new window in order to
• display a message
• ask for confirmation of an action
• request an input

• For these purposes, the window object in JavaScript provides
pre-defined methods for the handling of dialog boxes
(windows for simple dialogs):

• null alert(message_string)

• bool confirm(message_string)

• string prompt(message_string, default)

COMP284 Scripting Languages Lecture 17 Slide L17 – 8

Dynamic web pages using JavaScript Dialog boxes

Window object: Dialog boxes

• null alert(message_string)
• creates a message box displaying message_string
• the box contains an ‘OK’ button that the user will have to click

(alternatively, the message box can be closed)
for the execution of the remaining code to proceed

Example:

alert("Local time: " + (new Date). toString ())

COMP284 Scripting Languages Lecture 17 Slide L17 – 9

Dynamic web pages using JavaScript Dialog boxes

Window object: Dialog boxes

• bool confirm(message_string)
• creates a message box displaying message_string
• the box contains two buttons ‘Cancel’ and ‘OK’
• the function returns true if the user selects ‘OK’, false otherwise

Example:

var answer = confirm("Are you sure?")

COMP284 Scripting Languages Lecture 17 Slide L17 – 10

Dynamic web pages using JavaScript Dialog boxes

Window object: Dialog boxes

• string prompt(message_string, default)
• creates a dialog box displaying
message_string and an
input field

• if a second argument default
is given, default will be
shown in the input field

• the box contains two buttons
‘Cancel’ and ‘OK’

• if the user selects ‘OK’ then
the current value entered in
the input field is returned as a
string, otherwise null is
returned

Example:

var userName =

prompt("What is your name?",

"")

COMP284 Scripting Languages Lecture 17 Slide L17 – 11

Dynamic web pages using JavaScript Dialog boxes

Window object: Dialog boxes

• prompt() always returns a string, even if the user enters a number

• To convert a string to number the following functions can be used:
• number parseInt(string [,base])

– converts string to an integer number wrt numeral system base
– only converts up to the first invalid character in string
– if the first non-whitespace character in string is not a digit, returns NaN

• number parseFloat(string)
– converts string to a floating-point number
– only converts up to the first invalid character in string
– if the first non-whitespace character in string is not a digit, returns NaN

• number Number(string)
– returns NaN if string contains an invalid character

COMP284 Scripting Languages Lecture 17 Slide L17 – 12

Dynamic web pages using JavaScript Dialog boxes

Dialog boxes: Example

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/jsPrompt.html

COMP284 Scripting Languages Lecture 17 Slide L17 – 13

Dynamic web pages using JavaScript Input validation

User input validation

• A common use of JavaScript is the validation of user input
in a HTML form before it is processed:

• check that required fields have not been left empty
• check that fields only contain allowed characters or

comply to a certain grammar

• check that values are within allowed bounds

COMP284 Scripting Languages Lecture 17 Slide L17 – 14

Dynamic web pages using JavaScript Input validation

User input validation

1 function validateUser(field) {
2 if (field == "") return "No username entered\n"
3 else if (field.length < 5) 4 return "Username too short\n" 5 else if (/[^a-zA-Z0 -9_-]/. test(field )) 6 return "Invalid character in username\n" 7 else return "" 8 } 9 10 function validateEmail(field) { 11 if (field == "") return "No email entered\n" 12 else if (!(( field.indexOf(".") > 0) &&
13 (field.indexOf("@") > 0)) ||
14 /[^a-zA -Z0 -9.@_ -]/. test(field))
15 return "Invalid character in email\n"
16 else return ""
17 }

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/jsValidate.html

COMP284 Scripting Languages Lecture 17 Slide L17 – 15

Dynamic web pages using JavaScript Input validation

Window and Document objects

JavaScript provides two objects that are essential to the creation of
dynamic web pages and interactive web applications:

document object

• an object-oriented representation of a web page (HTML document) that
is displayed in a window

• allows interaction with the Document Object Model (DOM) of a page
Example: document.writeln() adds content to a web page

Document Object Model

A platform- and language-neutral interface that allows programs and
scripts to dynamically access and update the content, structure and style
of HTML, XHTML and XML documents

COMP284 Scripting Languages Lecture 17 Slide L17 – 16

Dynamic web pages using JavaScript Document object and Document Object Model

Document Object Model

Example:

The HTML table below

is parsed into the following DOM

Arnaud Le Hors, et al, editors: Document Object Model (DOM) Level 3 Core Specification, Version 1.0,
W3C Recommendation 07 April 2004. World Wide Web Consortium, 2004.
https://www.w3.org/TR/DOM-Level-3-Core/ [accessed 9 January 2017]

COMP284 Scripting Languages Lecture 17 Slide L17 – 17

Dynamic web pages using JavaScript Document object and Document Object Model

Accessing HTML elements: Object methods

Example:
// access the tbody element from the table element

var myTbodyElement = myTableElement.firstChild;

// access its second tr element; the list of children starts at 0 (not 1).

var mySecondTrElement = myTbodyElement.childNodes [1];

// remove its first td element

mySecondTrElement.removeChild(mySecondTrElement.firstChild );

// change the text content of the remaining td element

mySecondTrElement.firstChild.firstChild.data = "Peter";

⇒

COMP284 Scripting Languages Lecture 17 Slide L17 – 18

Dynamic web pages using JavaScript Document object and Document Object Model

Accessing HTML elements: Names (1)

Instead of using methods such as firstChild and childNodes[n], it is
possible to assign names to denote the children of a HTML element

Example:

Then – document.form1
Refers to the whole form

– document.form1.celsius
Refers to the text field named celsius in document.form1

– document.form1.celsius.value
Refers to the attribute value in the text field named celsius
in document.form1

COMP284 Scripting Languages Lecture 17 Slide L17 – 19

Dynamic web pages using JavaScript Document object and Document Object Model

Accessing HTML elements: Names (2)

Accessing HTML elements by giving them names and using paths within
the Document Object Model tree structure is still problematic
; If that tree structure changes, then those paths no longer work

Example:
Changing the previous form to

means that document.form1.celsius no longer works as there is now a
div element between form and text field, we would now need to use
document.form1.cdiv.celsius

COMP284 Scripting Languages Lecture 17 Slide L17 – 20

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/jsPrompt.html
http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/jsValidate.html
https://www.w3.org/TR/DOM-Level-3-Core/

Dynamic web pages using JavaScript Document object and Document Object Model

Accessing HTML elements: IDs

A more reliable way is to give each HTML element an ID
(using the id attribute) and to use getElementById to retrieve
a HTML element by its ID

Example:

Then
– document.getElementById(’celsius’)

Refers to the HTML element with ID celsius document
– document.getElementById(’celsius’).value

Refers to the attribute value in the HTML element with ID celsius
in document

COMP284 Scripting Languages Lecture 17 Slide L17 – 21

Dynamic web pages using JavaScript Document object and Document Object Model

Manipulating HTML elements

It is not only possible to access HTML elements, but also possible to
change them on-the-fly

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/jsBG.html

COMP284 Scripting Languages Lecture 17 Slide L17 – 22

Event-driven Programs Introduction

Event-driven JavaScript Programs

• The JavaScript programs we have seen so far
were all executed sequentially

• programs have a particular starting point
• programs are executed step-by-step,

involving control structures and function execution

• programs reach a point at which their execution stops

COMP284 Scripting Languages Lecture 17 Slide L17 – 23

Event-driven Programs Introduction

Event-Driven JavaScript Programs

• Web applications are event-driven
; they react to events such as mouse clicks and key strokes

nickywalters: What is Event Driven Programming?
SlideShare, 7 September 2014.
https://tinyurl.com/ya58xbs9 [accessed 5/11/2017]

• With JavaScript,
– we can define event handler functions for a wide variety of events
– event handler functions can manipulate the document object

(changing the web page in situ)

COMP284 Scripting Languages Lecture 17 Slide L17 – 24

Event-driven Programs Introduction

Event Handlers and HTML Elements

• HTML events are things, mostly user actions, that happen to HTML
elements

• Event handlers are JavaScript functions that process events
• Event handlers must be associated with HTML elements for specific

events
• This can be done via attributes

• Alternatively, a JavaScript function can be used to add a handler to an
HTML element

// All good browsers

window.addEventListener("load", Hello)

// MS IE browser

window.attachEvent("onload", Hello)

More than one event handler can be added this way to the same
element for the same event

COMP284 Scripting Languages Lecture 17 Slide L17 – 25

Event-driven Programs Introduction

Event Handlers and HTML Elements

• As our scripts should work with as many browsers as possible, we need
to detect which method works:

if (window.addEventListener) {

window.addEventListener("load", Hello)

} else {

window.attachEvent("onload", Hello)

}

• Event handlers can also be removed
if (window.removeEventListener) {

window.removeEventListener("load", Hello)

} else {

window.detachEvent("onload", Hello)

}

COMP284 Scripting Languages Lecture 17 Slide L17 – 26

Event-driven Programs Introduction

Events: Load

• An (on)load event occurs when an object has been loaded
• Typically, event handlers for onload events are associated with the

window object or the body element of an HTML document

Content of the web page

http://cgi.csc.liv.ac.uk/~ullrich/COMP519/examples/jsOnload.html

COMP284 Scripting Languages Lecture 17 Slide L17 – 27

Event-driven Programs Events

Events: Focus / Change

• A focus event occurs when a form field receives input focus by tabbing
with the keyboard or clicking with the mouse
; onFocus attribute

• A change event occurs when a select, text, or textarea field loses focus
and its value has been modified
; onChange attribute

Example:

COMP284 Scripting Languages Lecture 17 Slide L17 – 28

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/jsBG.html
https://tinyurl.com/ya58xbs9
http://cgi.csc.liv.ac.uk/~ullrich/COMP519/examples/jsOnload.html

Event-driven Programs Events

Events: Focus / Change

• A focus event occurs when a form field receives input focus by tabbing
with the keyboard or clicking with the mouse
; onFocus attribute

• A change event occurs when a select, text, or textarea field loses focus
and its value has been modified
; onChange attribute

http://cgi.csc.liv.ac.uk/~ullrich/COMP519/examples/jsOnchange.html

COMP284 Scripting Languages Lecture 17 Slide L17 – 29

Event-driven Programs Events

Events: Blur / Click

• A blur event occurs when an HTML element loses focus
; onBlur attribute

• A click event occurs when an object on a form is clicked
; onClick attribute

Example:

http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/jsOnclick.html

COMP284 Scripting Languages Lecture 17 Slide L17 – 30

Event-driven Programs Events

Events: MouseOver / Select / Submit

• A keydown event occurs when the user presses a key
; onkeydown attribute

• A mouseOver event occurs once each time the mouse pointer moves
over an HTML element from outside that element
; onMouseOver attribute

• A select event occurs when a user selects some of the text within a text
or textarea field
; onSelect attribute

• A submit event occurs when a user submits a form
; onSubmit attribute

COMP284 Scripting Languages Lecture 17 Slide L17 – 31

Event-driven Programs Events

Events and DOM

• When an event occurs, an event object is created
; an event object has attributes and methods
; event objects can be created by your code

independent of an event occurring

• In most browsers, the event object is passed to event handler functions
as an argument

• In most versions of Microsoft Internet Explorer, the most recent event
can only be accessed via window.event

COMP284 Scripting Languages Lecture 17 Slide L17 – 32

Event-driven Programs Events

Revision

Read

• Chapter 17: JavaScript and PHP Validation and Error Handling
• Chapter 18: Using Ajax
of

R. Nixon:
Learning PHP, MySQL, and JavaScript.
O’Reilly, 2009.

• Mozilla Developer Network and individual contributors:
Document Object Model (DOM), 18 March 2014.
https://developer.mozilla.org/en/docs/DOM

[accessed 18 March 2014].

• W3Schools: JavaScript and HTML DOM Reference,
18 March 2014. http://www.w3schools.com/jsref/
[accessed 18 March 2014].

COMP284 Scripting Languages Lecture 17 Slide L17 – 33

http://cgi.csc.liv.ac.uk/~ullrich/COMP519/examples/jsOnchange.html
http://cgi.csc.liv.ac.uk/~ullrich/COMP284/examples/jsOnclick.html
https://developer.mozilla.org/en/docs/DOM
http://www.w3schools.com/jsref/

Lecture 1
Introduction
Motivation
Scripting languages

COMP284
Aims
Learning outcomes
Delivery
Assessment

Lecture 2
Perl: Overview
History
Applications
Java vs Perl

Scalars
Definition
Integers and Floating-point numbers
Strings
`Booleans'
Comparisons

Variables, Constants, and Assignments
Variables
Constants
Assignments
Variable interpolation

Lecture 3
Control structures
Conditional statements
Switch statements
While- and Until-loops
For-loops

Lists and Arrays
Identifiers
List literals
Contexts
List and array functions
Foreach-loops

Hashes
Identifiers
Basic hash operations
Foreach

Lecture 4
Regular expressions (1)
Introduction
Characters
Character classes
Quantifiers

Lecture 5
Regular expressions (2)
Capture groups
Alternations
Anchors
Modifiers
Binding operator

Lecture 6
Substitution
Binding operators
Capture variables
Modifiers

Subroutines
Introduction
Defining a subroutine
Parameters and Arguments
Calling a subroutine
Persistent variables
Nested subroutine definitions

Lecture 7
Input/Output
Filehandles
Open
Close
Read
Select
Print
Here documents

Arguments and Options
Invocation Arguments
Options

Lecture 8
CGI
Overview
CGI I/O

The Perl module CGI.pm
Motivation
HTML shortcuts
Forms

Lecture 9
PHP
Motivation

Overview
Features
Applications

Types and Variables
Types
Variables
Type juggling and Type casting
Comparisons

Lecture 10
Scalar types
Integers and Floating-point numbers
Exceptions and error handling
Booleans
Strings

Compound types
Arrays
Foreach-loops
Array functions

Printing

Lecture 11
Special types
NULL
Resources

Control structures
Conditional statements
Switch statements
While- and Do While-loops
For-loops

Functions
Defining a function
Calling a function
Variables
Functions and HTML
Variable-length argument lists

PHP libraries
Include/Require

Lecture 12
Web applications
Overview
HTML forms

Available information and Input
Overview
PHP environment
Server variables
Form data

PHP sessions
Start a PHP session
Maintain session data
End a PHP session
Session management
Example

Authentication
Overview
Example

Lecture 13
Classes
Defining and Instantiating a Class
Visibility
Class Constants
Static Properties and Methods
Destructors
Inheritance
Interfaces
Introspection Functions

The PDO Class
Introduction
Connections
Queries and Processing of Results
Prepared Statements
Transactions

Lecture 14
JavaScript
Motivation
Overview
Example

Types and Variables
Types
Variables
Typecasting
Comparisons

Lecture 15
Primitive datatypes
Numbers
Booleans
Strings

Arrays
Definition
forEach-method
Array functions

Control structures
Conditional statements
Switch statements
While- and Do While-loops
For-loops

Lecture 16
Functions
Defining a function
Calling a function
Variable-length argument lists
Static variables
Example
Nested function definitions

JavaScript libraries
(User-defined) Objects
Object Literals
Object Constructors
Definition and use
Prototype property
Public and private static variables
Pre-defined objects

Lecture 17
Dynamic web pages using JavaScript
Window and Document objects
Window object: Properties and methods
Dialog boxes
Input validation
Document object and Document Object Model

Event-driven Programs
Introduction
Events