Cours Perl

8/6/2019 Cours Perl

1/120

London Perl Workshop

1st December 20071

Beginners Perl

An Introduction to Perl Programming

Dave Cross

Magnum Solutions Ltd

[email protected]

8/6/2019 Cours Perl

2/120


1st December 20072

What

W

eW

ill Cover What is Perl?

Creating and running a Perl program Perl variables

Operators and Functions

8/6/2019 Cours Perl

3/120


1st December 20073

WhatW

eW

ill Cover Conditional Constructs

Subroutines

Regular Expressions

Further Information

8/6/2019 Cours Perl

4/120


1st December 20074

What is Perl?

8/6/2019 Cours Perl

5/120


1st December 20075

Perl's Nam

e Practical Extraction and Reporting

Language

Pathologically Eclectic Rubbish Lister

"Perl" is the language

"perl" is the compiler

Never "PERL"

8/6/2019 Cours Perl

6/120


1st December 20076

Typica

l uses of Perl Text processing

System administration tasks CGI and web programming

Database interaction

Other Internet programming

8/6/2019 Cours Perl

7/120


1st December 20077

Lesstypic

al uses of Perl

Human Genome Project

NASA

8/6/2019 Cours Perl

8/120


1st December 20078

What

is PerlLike?

General purpose programming language

Free (open source) Fast

Flexible

Secure

Dynamic

8/6/2019 Cours Perl

9/120


1st December 20079

Th

e Perl Ph

ilosophy

There's more than one way to do it

Three virtues of a programmer Laziness

Impatience

Hubris

Share and enjoy!

8/6/2019 Cours Perl

10/120


1st December 200710

Creating and Running aPerl Program

8/6/2019 Cours Perl

11/120


1st December 200711

Creat

inga

Perl Program

Our first Perl programprint "Hello world\n";

Put this in a file called hello.pl

8/6/2019 Cours Perl

12/120


1st December 200712

Runninga

Perl Program

Running a Perl program from the command

line

perl hello.pl

8/6/2019 Cours Perl

13/120


1st December 200713

Runninga

Perl Program

The "shebang" line (Unix, not Perl)#!/usr/bin/perl

Make program executablechmod +x hello.pl

Run from command line./hello.pl

8/6/2019 Cours Perl

14/120


1st December 200714

Perl Comm

ent

s Add comments to yout code

Start with a hash (#) Continue to end of line

# This is a hello world program

print "Hello, world!\n"; # print

8/6/2019 Cours Perl

15/120


1st December 200715

Comma

ndLine Op

t

ions Many options to control execution of the

program For example, -w turns on warnings

Use on command lineperl -w hello.pl

Or on shebang line#!/usr/bin/perl -w

8/6/2019 Cours Perl

16/120


1st December 2007

16

Perl variables

8/6/2019 Cours Perl

17/120


1st December 2007

17

What

isa

Va

riab

le? A place where we can store data

A variable needs a name to retrieve the data stored in it

put new data in it

8/6/2019 Cours Perl

18/120


1st December 2007

18

Va

riab

le Nam

es Contain alphanumeric characters and

underscores

User variable names may not start with

numbers

Variable names are preceded by apunctuation mark indicating the type of

data

8/6/2019 Cours Perl

19/120


1st December 2007

19

Types of Perl Va

riab

le Different types of variables start with a

different symbol

Scalar variables start with $

Array variables start with @

Hash variables start with %

More on these types soon

8/6/2019 Cours Perl

20/120


1st December 2007

20

Decl

a

ring Va

riab

les You don't need to declare variables in Perl

But it's a very good idea typos

scoping

Using the strict pragmause strict;

my $var;

8/6/2019 Cours Perl

21/120


1st December 2007

21

Sca

la

r Va

riab

les Store a single item of data my $name = "Dave";

my $whoami = 'Just Another Perl

Hacker';

my $meaning_of_life = 42;

my $number_le

ss_than_1 = 0.000001;

my $very_large_number = 3.27e17;

# 3.27 times 10 to the power of 17

8/6/2019 Cours Perl

22/120


1st December 2007

22

Type Conversions Perl converts between strings and numbers

whenever necessary

# add int to a floating point number

my $sum = $meaning_of_life +

$number_less_than_1;

#putting the n

umber in a

stringprint "$name says, 'The meaning of

life is $sum.'\n";

8/6/2019 Cours Perl

23/120


1st December 2007

23

Quot

ingSt

rings Single quotes don't expand variables or

escape sequencesmy $price = '$9.95';

Double quotes domy $invline = "24 widgets @ $price

each\n";

Use a backslash to escape special

characters in double quoted stringsprint "He said \"The price is \$300\"";

8/6/2019 Cours Perl

24/120


1st December 2007

24

Bett

erQ

uot

e Ma

rks This can look ugly

print "He said \"The price is \$300\"";

This is a tidier alternative

print qq(He said "The price is \$300");

Also works for single quotes

print q(He said "That's too expensive");

8/6/2019 Cours Perl

25/120

8/6/2019 Cours Perl

26/120

8/6/2019 Cours Perl

27/120

8/6/2019 Cours Perl

28/120


1st December 2007

28

A

rra

yS

lices Returns a list of elements from an array

print @fruits[0,2,4];

# prints "apples", "guavas",

# "grapes"

print @fruits[1 .. 3];

# prints "oranges", "guavas",

# "passionfruit"

Note use of @ as we are accessing more

than one element of the array

8/6/2019 Cours Perl

29/120


1st

December 2007

29

S

ett

ingA

rray

Va

lues $array[4] = 'something';

$array[400] = 'something else';

Also with slices @array[4, 7 .. 9] = ('four', 'seven',

'eight', 'nine');

@array[1, 2] = @array

[2, 1];

Doesn't need to be an array! ($x, $y) = ($y, $x);

8/6/2019 Cours Perl

30/120


1st

December 2007

30

ArraySize

$#array is the index of the last element

in @array

Therefore $#array + 1 is the number of

elements $count = @array;

# or $count = scalar @arraydoes the same thing and is easier to

understand

8/6/2019 Cours Perl

31/120


1st

December 2007

31

Hash Variables

Hashes implement look-up tables or

dictionaries

Initialised with a list%french = ('one', 'un', 'two', 'deux',

'three', 'trois');

"fat comma" (=>) is easier to understand%german = (one => 'ein',two => 'zwei',

three => 'drei');

8/6/2019 Cours Perl

32/120


1st

December 2007

32

Accessing Hash Values

$three = $french{three};

print $german{two}; As with arrays, notice the use of $ to

indicate that we're accessing a single value

8/6/2019 Cours Perl

33/120


1st

December 2007

33

HashSlices

Just like array slices

Returns a list of elements from a hashprint @french{'one','two','three'};# prints "un", "deux" & "trois"

Again, note use of @ as we are accessing

more than one value from the hash

8/6/2019 Cours Perl

34/120

8/6/2019 Cours Perl

35/120


1st

December 2007

35

More AboutHashes

Hashes are not sorted

There is no equivalent to $#array print %hash is unhelpful

We'll see ways round these restrictions later

8/6/2019 Cours Perl

36/120


1st

December 2007

36

Special Perl Variables

Perl has many special variables

Many of them have punctuation marks asnames

Others have names in ALL_CAPS

They are documented in perlvar

8/6/2019 Cours Perl

37/120

8/6/2019 Cours Perl

38/120


1st

December 2007

38

Using $_

while () {if (/regex/) {

print;}}

Three uses of $_

8/6/2019 Cours Perl

39/120


1st

December 2007

39

ASpecial Array

@ARGV

Contains your program's command linearguments

perl printargs.pl foo bar baz

my $num = @ARGV;print "$num arguments: @ARGV\n";

8/6/2019 Cours Perl

40/120


1st

December 2007

40

ASpecial Hash

%ENV

Contains the environment variables thatyour script has access to.

Keys are the variable names

Values are the well values! print $ENV{PATH};

8/6/2019 Cours Perl

41/120


1st

December 2007

41

Operators and Functions

8/6/2019 Cours Perl

42/120

8/6/2019 Cours Perl

43/120


1st

December 2007

43

Arithmetic Operators

Standard arithmetic operationsadd (+), subtract (-), multiply (*), divide (/)

Less standard operationsmodulus (%), exponentiation (**)

$speed = $distance / $time;

$vol = $length * $breadth * $height;$area = $pi * ($radius ** 2);$odd = $number % 2;

8/6/2019 Cours Perl

44/120


1st

December 2007

44

Shortcut Operators

Often need to do things like$total = $total + $amount;

Can be abbreviated to$total += $amount;

Even shorter$x++; #same as $x += 1 or $x = $x + 1

$y--; #same as $y -= 1 or $y = $y - 1

Subtle difference between $x++ and ++$x

8/6/2019 Cours Perl

45/120


1st

December 2007

45

String Operators

Concaternation (.)$name = $firstname . ' ' . $surname;

Repetition (x)$line = '-' x 80;$police = 'hello ' x 3;

Shortcut versions available$page .= $line; # $page = $page . $line$thing x= $i; # $thing = $thing x $i

8/6/2019 Cours Perl

46/120

8/6/2019 Cours Perl

47/120

8/6/2019 Cours Perl

48/120

8/6/2019 Cours Perl

49/120


1st

December 2007

49

String Functions

length returns the length of a string$len = length $a_string;

uc and lc return upper and lower caseversions of a string$string = 'MiXeD CaSe';print "$string\n", uc $string, "\n",

lc $string;

See also ucfirst and lcfirst

8/6/2019 Cours Perl

50/120

8/6/2019 Cours Perl

51/120


1st

December 2007

51

Substrings

substr returns substrings from a string$string = 'Hello world';

printsubs

tr($string, 0, 5);# prints 'Hello'

Unlike many other languages you canassign to a substring

substr($string, 0, 5) = 'Greetings';print $string;# prints 'Greetings world'

8/6/2019 Cours Perl

52/120

8/6/2019 Cours Perl

53/120

8/6/2019 Cours Perl

54/120

8/6/2019 Cours Perl

55/120

8/6/2019 Cours Perl

56/120

8/6/2019 Cours Perl

57/120


1

st

December 2007

57

File Operations

open opens a file and associates it with afilehandle

open(FILE, 'in.dat'); You can then read the file with $line = ; # one line@lines = ; # all lines

Finally, close the file with closeclose(FILE);

8/6/2019 Cours Perl

58/120


1

st

December 2007

58

Other File Functions

read to read a fixed number of bytes into abuffer

$bytes = read(FILE, $buffer, 1024);

seek to move to a random postion in a fileseek(FILE, 0, 0);

tell to get current file position$where = tell FILE;

truncate to truncate file to given sizetruncate FILE, $where;

8/6/2019 Cours Perl

59/120

8/6/2019 Cours Perl

60/120


1

st

December 2007

60

localtime Caveats

$mon is 0 to 11

$year is years since 1900

$wday is 0 (Sun) to 6 (Sat)

8/6/2019 Cours Perl

61/120

8/6/2019 Cours Perl

62/120

London Perl Workshop1st December 2007

62

Conditional Constructs

Conditional constructs allow us to choosedifferent routes of execution through the

program This makes for far more interesting

programs

The unit of program execution is a blockofcode

Blocks are delimited with braces { }

8/6/2019 Cours Perl

63/120


63

Conditional Constructs

Conditional blocks are controlled by theevaluation of an expression to see if it is

true or false But what is truth?

8/6/2019 Cours Perl

64/120


64

What is Truth?

In Perl it's easier to answer the question"what is false?"

0 (the number zero) '' (the empty string)

undef (an undefined value)

() (an empty list) Everything else is true

8/6/2019 Cours Perl

65/120


65

Comparison Operators

Compare two values in some way are they equal

$x == $y or$x eq $y$x != $y or$x ne $y

Is one greater than another$x > $y or$x gt $y

$x >= $y or$x ge $y Also < (lt) and

8/6/2019 Cours Perl

66/120

8/6/2019 Cours Perl

67/120


67

Boolean Operators

Combine two or more conditionalexpressions into one

EXPR_1 and EXPR_2true if both EXPR_1 and EXPR_2 are true

EXPR_1 or _EXPR_2

true if either EXPR_1 or _EXPR_2 are true

alternative syntax && forand and || foror

8/6/2019 Cours Perl

68/120

8/6/2019 Cours Perl

69/120


69

if

if - our first conditional

if (EXPR) { BLOCK }

Only executes BLOCK if EXPR is trueif ($name eq 'Doctor') {regenerate();

}

8/6/2019 Cours Perl

70/120


70

if ... else ...

if else ... - an extended ifif (EXPR) { BLOCK1 } else { BLOCK2}

If EXPR is true, execute BLOCK1,otherwise execute BLOCK2

if ($name eq 'Doctor') {regenerate();

} else {die "Game over!\n";

}

8/6/2019 Cours Perl

71/120

8/6/2019 Cours Perl

72/120

8/6/2019 Cours Perl

73/120


73

while

while - repeat the same codewhile (EXPR) { BLOCK}

Repeat BLOCKwhile EXPR is truewhile ($dalek_prisoners) {print "Ex-ter-min-ate\n";$dalek_prisoners--;

}

8/6/2019 Cours Perl

74/120


74

until

until - the opposite of whileuntil (EXPR) { BLOCK}

Execute BLOCKuntil EXPR is trueuntil ($regenerations == 12) {print "Regenerating\n";regenerate();$regenerations++;

}

8/6/2019 Cours Perl

75/120

8/6/2019 Cours Perl

76/120


76

for

An examplefor ($i = 1; $i

8/6/2019 Cours Perl

77/120


77

foreach

foreach - simpler looping over listsforeach VAR (LIST) { BLOCK}

For each element of LIST, set VAR toequal the element and execute BLOCKforeach $i (1 .. 10) {print "$i squared is ",

$i * $i, "\n";}

8/6/2019 Cours Perl

78/120


78

foreach

Another examplemy %months = (Jan => 31, Feb => 28,

Mar => 31, Apr => 30,May => 31, Jun => 30, );

foreach (keys%months) {print "$_ has $months{$_} days\n";

}

8/6/2019 Cours Perl

79/120


79

Using while Loops

Taking input from STDIN

while () {

print;}

This is the same as

while (defined($_ = )) {print $_;}

8/6/2019 Cours Perl

80/120


80

Breaking Out ofLoops

next - jump to next iteration of loop

last - jump out of loop

redo - jump to start ofsame iteration ofloop

8/6/2019 Cours Perl

81/120


81

Subroutines

8/6/2019 Cours Perl

82/120


82

Subroutines

Self-contained "mini-programs" withinyour program

Subroutines have a name and a block ofcode

sub NAME {BLOCK

}

8/6/2019 Cours Perl

83/120


83

Subroutine Example

Simple subroutine examplesub exterminate {

print "Ex-Ter

-Min

-Ate!!\n";$timelords--;

}

8/6/2019 Cours Perl

84/120


84

Calling aSubroutine

&slay;

slay();

slay;

last one only works if function has beenpredeclared

8/6/2019 Cours Perl

85/120


85

Subroutine Arguments

Functions become far more useful if youcan pass arguments to them

exterminate('The Doctor'); Arguments end up in the @_ array within

the functionsub exterminate {

my ($name) = @_;print "Ex-Ter-Min-Ate $name\n";$timelords--;

}

8/6/2019 Cours Perl

86/120


86

Multiple Arguments

As @_ is an array it can contain multiplearguments

sub exterminate {foreach (@_) {print "Ex-Ter-Min-Ate $_\n";$timelords--;

}}

8/6/2019 Cours Perl

87/120


87

Calling Subroutines

A subtle difference between &my_sub andmy_sub()

&my_subpasses on the contents of@_ tothe called subroutinesub first { &second };subsecond { print @_ };

first('some', 'random', 'data');

8/6/2019 Cours Perl

88/120


88

By Value or Reference

Passing by value passes the value of thevariable into the subroutine. Changing the

argument doesn't alter the external variable Passing by value passes the actualvariable.

Changing the argument alters the externalvalue

Perl allows you to choose

8/6/2019 Cours Perl

89/120


89

By Value or Reference

Simulating pass by valuemy ($arg1, $arg2) = @_;

Updating $arg1 and $arg2 doesnt effectanything outside the subroutine

Simulating pass by referenceUpdating the contents of@_ updates the

external values$_[0] = 'whatever';

8/6/2019 Cours Perl

90/120


90

Returning Values

Use return to return a value from asubroutine

sub exterminate {if (rand > .25) {print "Ex-Ter-Min-Ate $_[0]\n";$timelords--;return 1;

} else {return;}

}

8/6/2019 Cours Perl

91/120


91

Returning aList

Returning a list from a subroutinesub exterminate {my @exterminated;

foreach (@_) {if (rand > .25) {print "Ex-Ter-Min-Ate $_\n";$timelords--;push @exterminated, $_;

}

}return @exterminated;

}

8/6/2019 Cours Perl

92/120


92

Regular Expressions

8/6/2019 Cours Perl

93/120


93

Regular Expressions

Patterns that match strings

A bit like wild-cards

A "mini-language" within Perl (AlienDNA)

The key to Perl's text processing power

Sometimes overused! Documented in perldoc perlre

8/6/2019 Cours Perl

94/120


94

Match Operator

m/PATTERN/ - the match operator

works on $_ by default

in scalar context returns true if the matchsucceeds

in list context returns list of "captured" text

m is optional if you use / characters with m you can use any delimiters

8/6/2019 Cours Perl

95/120


95

Match Examples

m/PATTERN/ examples

while () {

print if /foo/;print if /bar/i;print if m|http://|;

}

8/6/2019 Cours Perl

96/120


96

Substitutions

s/PATTERN/REPLACEMENT/ - thesubstitution operator

works on $_ by default in scalar context returns true if substitution

succeeds

in list context returns number ofreplacements

can choose any delimiter

8/6/2019 Cours Perl

97/120


97

Substitution Examples

s/PATTERN/REPLACEMENT/ examples

while () {

s/teh/the/gi;s/freind/friend/gi;s/sholud/should/gi;print;

}

8/6/2019 Cours Perl

98/120


98

Binding Operator

If we want m// ors/// to work onsomething other than $_ then we need to

use the binding operator $name =~ s/Dave/David/;

8/6/2019 Cours Perl

99/120


99

Metacharacters

Matching something other than literal text

^ - matches start of string

$ - matches end of string

. - matches any character (except \n)

\s - matches a whitespace character

\S - matches a non-whitespace character

8/6/2019 Cours Perl

100/120


100

More Metacharacters

\d - matches any digit

\D - matches any non-digit

\w - matches any "word" character

\W - matches any "non-word" character

\b - matches a word boundary

\B - matches anywhere except a wordboundary

8/6/2019 Cours Perl

101/120


101

Metacharacter Examples

while () {print if m|^http|;

print if /\bperl\b/;print if /\S/;print if /\$\d\.\d\d/;

}

8/6/2019 Cours Perl

102/120


102

Quantifiers

Specify the number of occurrences

? - match zero or one

* - match zero or more

+ - match one or more

{n} - match exactly n

{n,} - match n or more

{n,m} - match between n and m

8/6/2019 Cours Perl

103/120


103

Quantifier Examples

while () {print if /whiske?y/i;

print if /so+n/;print if /\d*\.\d+/;print if /\bA\w{3}\b/;

}

8/6/2019 Cours Perl

104/120


104

Character Classes

Define a class of characters to match

/[aeiou]/# match any vowel

Use - to define a contiguous set /[A-Z]/# match upper caseletters

Use ^ to match inverse set /[^A-Za-z] # match non-letters

8/6/2019 Cours Perl

106/120


106

Capturing Matches

Parentheses are also used to capture partsof the matched string

The captured parts are in $1, $2, etcwhile () {if (/^(\w+)\s+(\w+)/) {print "The first word was $1\n";

print "Thesec

ond word was$2";}

}

8/6/2019 Cours Perl

107/120


107

Returning Captures

Captured values are also returned if thematch operator is used in list context

my @nums = $text =~ /(\d+)/g;print "I found these integers:\n";print "@nums\n";

8/6/2019 Cours Perl

108/120


108

More Information

8/6/2019 Cours Perl

109/120


109

Perl Websites

Perl Home Page http://www.perl.org

CPAN http://www.cpan.org

http://search.cpan.org

Perl Mongers (Perl User Groups) http://www.pm.org

http://london.pm.org

8/6/2019 Cours Perl

110/120


110

Perl Websites

use perl;(Perl news site) http://use.perl.org

Perl Monks (Perl help and advice) http://www.perlmonks.org

Perl documentation online http://perldoc.perl.org

8/6/2019 Cours Perl

111/120


111

Perl Conferences

The Perl Conference(part of the Open Source Convention)

July, 21-25 2008 Portland, Oregon http://conferences.oreilly.com

Yet Another Perl Conference 2008 Copenhagen, Denmark

http://www.yapceurope.org

8/6/2019 Cours Perl

112/120


112

Perl Conferences OtherYAPCs

Chicago, Illinois

Brazil

Tokyo

OSDC

Israel

Australia

8/6/2019 Cours Perl

113/120


113

Perl Workshops One-day grassroots conferences

Like this one

Germany, Israel, Pittsburgh, Nordic,Netherlands, France, Belgium, Russia,Minnesota, Austria

Perl Review Calendar

www.theperlreview.com/community_calendar

8/6/2019 Cours Perl

114/120

8/6/2019 Cours Perl

115/120

P l B k

8/6/2019 Cours Perl

116/120


116

Perl Books

Books you should have access to Programming Perl (3rd edition)

Wall, Christiansen & Orwant (O'Reilly) The Perl Cookbook (2nd edition)

Christiansen & Torkington (O'Reilly)

Perl Best PracticesConway (O'Reilly)

Perl in a NutshellSiever, Spainhour & Patwardhan (O'Reilly)

P l B k

8/6/2019 Cours Perl

117/120


117

Perl Books

Books you should probably look at Mastering Regular Expressions

Friedl (O'Reilly)

Data Munging with PerlCross (Manning)

Advanced Perl ProgrammingCozens (O'Reilly)

Perl MedicScott (Addison Wesley)

P l B k

8/6/2019 Cours Perl

118/120


118

Perl Books

Specialised Perl books Object Oriented Perl

Conway (Manning) Programming the Perl DBI

Descartes & Bunce (O'Reilly)

Writing CGI Applications with PerlMeltzer & Michelski (Addison Wesley)

Practical mod_perlBekman & Cholet (O'Reilly)

P l M i

8/6/2019 Cours Perl

119/120


119

Perl Magazines

The Perl Review http://www.theperlreview.com

8/6/2019 Cours Perl

120/120

That's All Folks Questions

Lunchtime

Documents

Cours Perl