practical extraction and report language perl - vital-it · perl's cgipm module, part of...

VI, October 2006

Practical Extraction and Report Language

« Perl is a language of getting your job done »

Larry Wall

« There is more than one way to do it »

Page 2VI, October 2006

Perl

History

Structure of a simple Perl script

Perl variables

scalar ($)

array (@)

hash (%)

Operators (numeric, string & logical)

Statement modifiers (if/elsif/else, for/foreach, while)

Outline :

VI, October 2006

Practical Extraction and Report Language

http://perl.oreilly.com

" Perl is both a programming language

and an application on your computer that runs those programs "


Perl history

1969 UNIX was born at Bell Labs.

1970 Brian Kernighan suggested the name "Unix" and the operating

system we know today was born.

1972 The programming language C is born at the Bell Labs

(C is one of Perl's ancestors).

1973 “grep” is introduced by Ken Thompson as an external utility:

Global REgular expression Print.

1976 Steven Jobs and Steven Wozniak found Apple Computer (1 April).

1977 The computer language awk is designed by Alfred V. Aho, Peter J.

Weinberger, and Brian W. Kernighan (awk is one of Perl's ancestors).

A few dates:

VI, October 2006

Perl history

1987 Perl 1.000 is unleashed upon the world

NAME perl | Practical Extraction and Report Language

SYNOPSIS perl [options] filename args

DESCRIPTION Perl is a interpreted language optimized for scanning arbitrary text

files, extracting information from those text files, and printing reports based on that

information. It's also a good language for many system management tasks. The language

is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny,

elegant, minimal). It combines (in the author's opinion, anyway) some of the best features

of C, sed, awk, and sh, so people familiar with those languages should have little difficulty

with it (Language historians will also note some vestiges of csh, Pascal, and even

BASIC|PLUS). Expression syntax corresponds quite closely to C expression syntax. If

you have a problem that would ordinarily use sed or awk or sh, but it exceeds their

capabilities or must run a little faster, and you don't want to write the silly thing in C, then perl

may be for you. There are also translators to turn your sed and awk scripts into perl scripts

OK, enough hype.


Perl history

1994 Perl5: last major release (Currently Perl 5.8.6).

1996 Creation of the CPAN repository of modules and documentation

( Comprehensive Perl Archive Network).

2006 Perl 5.8.8

Supported Operating Systems:

Unix systems / Macintosh (OS 7-9 and X) / Windows / VMS

Perl Features

Perls database integration interface (DBI) supports thirdparty databases

including Oracle, Sybase, Postgres, MySQL and others.

Perl works with HTML, XML, and other markup languages .

Perl supports Unicode.

Perl is Y2K compliant.

Perl supports both procedural and objectoriented programming.

Perl interfaces with external C/C++ libraries through XS or SWIG.

Perl is extensible There are over 500 third party modules available from

(CPAN).

VI, October 2006

Perl history

Perl and the Web

Perl is the most popular web programming language due to its text

manipulation capabilities and rapid development cycle.

Perl's CGIpm module, part of Perl's standard distribution, makes handling

HTML forms simple.

Perl can handle encrypted Web data, including ecommerce transactions.

Perl can be embedded into web servers (mod_perl) to speed up processing

by as much as 2000%.

Perl's DBI package makes webdatabase integration easy.


Perl Hello world !

My first program (hello.pl) :

pcX: vioannid$ which perl

/usr/bin/perl

pcY: vioannid$ which perl

/usr/local/bin/perl

#!/usr/local/bin/perl

use strict;

use warnings;

#tell the program to print "Hello world"

print "Hello world" ;

#tell the program to exit

exit ;

The first line of a Perl program is called "command interpretation" or "Shebang line". This line

refers to the "#!" and tells the computer that this is a Perl program.

To find out whether you should use /usr/bin/perl OR /usr/local/bin/perl,

type: "which perl" in your shell:

VI, October 2006

Perl Hello world !


computerX: vioannid$ which perl

/usr/bin/perl

computerY: vioannid$ which perl

/usr/local/bin/perl


use strict;

use warnings;




exit ;

perl script

UNIX shell

[embnet01@bc2-linux3 ~]$ which perl

/import/bc2/soft/bin/perl5/perl

#!/import/bc2/soft/bin/perl5/perl


Perl Hello world !


use strict;

A command like use strict is called a pragma. Pragmas are instructions to the Perl interpreter to do

something special when it runs your program. "use strict" does two things that make it harder to

write bad software:

It makes you declare all your variables, and

it makes it harder for Perl to mistake your intentions when you are using subroutines

ALL STATEMENTS END IN A SEMICOLON ";"

(similar to the use of the period "." in the English language)


use strict;

use warnings;

#tell the program to print "Hello world "



exit ;

VI, October 2006

Perl Hello world !



use strict;

use warnings;




exit ;

use warnings;

Comments are good, but the most important tool for writing good Perl is the "warnings". Turning on

warnings will make Perl yelp and complain at a huge variety of things that are almost always

sources of bugs in your programs.

Perl normally takes a relaxed attitude toward things that may be problems:

it assumes that you know what you're doing, even when you don't…


Perl Hello world !



use strict;

use warnings;




exit ;

Comments

All lines starting with "#" are not taken into account in the execution of the program.

Good comments are short, but instructive. They tell you things that aren't clear from reading

the code.

Blank lines or spaces are also not taken into account in the execution of the program. However, they

help in the reading of the code.

VI, October 2006

Perl Hello world !



use strict;

use warnings;




exit ;

Print statement:

… prints !

By default, the standard output is the shell window from which the program is executed.

ALL STATEMENTS ENDS IN A SEMICOLON ";"

(similar to the use of the period "." in the English language)


Perl Hello world !



use strict;

use warnings;




exit ;

The exit statement:

Tells the computer to exit the program.

Although not explicitely required in Perl, it is definitely common.

VI, October 2006

Perl Hello world !



use strict;

use warnings;




exit ;

Do not forget to make the file executable:

output:

vioannid$ ./hello.pl

Hello worldvioannid$

vioannid$ chmod a+x hello.pl


Perl Hello world !!

Print :


use strict;

use warnings;

#play with the print statement

#words separated by newline

print "Hello\nworld\n" ;

#words separated by tabs & a final newline

print "Hello\tworld\n" ;

#usage of the period to cat strings

print "Hello"."world"."\n";


exit ;

vioannid$ ./hello2.pl

Hello

world

Hello world

Helloworld

vioannid$

Important:

Unix & all Unix flavors: \n

Mac OS : \r

Windows: \r\n

VI, October 2006

Perl variables and data types

Type Character Example Is a name for:

Scalar $ $gene_symbol An individual value (number or string)

Array @ @sequences A list of values, keyed by number

Hash % %descriptions A group of values, keyed by string

Subroutine & &align A callable chunk of Perl code

Typeglob * *protein Everything named protein

Variables are containers which can hold data of a various types


Perl variables - Scalars

scalars

a single string (of any size, limited only by the available memory), or

a number (integers, floating-point numbers), or

a boolean (true or false or 0 or 1), or

a reference to something

The “beauty” of PERL is that you don’t declare your scalar variables to be of a certain data type,

Perl figures it out for you ! Depending on the CONTEXT, Perl will automatically interpret them as

strings, as numbers, or as boolean values (true or false).

Scalar values are always named with '$' (even when referring to a scalar that is part of an array or

a hash). The '$' symbol works semantically like the English word "the" in that it indicates a single

value is expected.

my $variable_1 = "Hello world !\n"; #note the quotes

my $variable_two = 30; #note the absence of quotes

VI, October 2006


Numeric

my $pi = 3.14159; # floating point number

my $avogadro = 6.02e23; # scientific notation

my $cash = 33651235421; # huge integer

my $cash2 = 33_651_235_421; # huge integer with underlines for visibility

my $result = 25; # integer

Numeric operators

1 + 1 # 1 plus 1, or 2

2.5 - 1.5 # 2.5 minus 1.5, or 1

2 * 6 # 2 times 6, or 12

14 / 2 # 14 divided by 2, or 7

10.2 / 3.14159 # 10.2 divided by 3.14159, or 3.24676358149854

10 % 3 # 10 modulo 3, or 1

10 / 3 # 10 divided by 3, or 3.333333333 (ALWAYS floating-point)

2 ** 3 # 2 to the power 3, or 8

my $total = $result + $cash2; # $total has now the value: 33651235446



Strings (sequences of characters)

' … ' (or q//) #no variable and backslash interpolation

my $name = 'Vassilios'; #literal string

my $hello = 'hello\tsir!'; #if printed, outputs: hello\tsir

my $cost = 'The meeting costs $100' ; #if printed, outputs: The meeting costs $100

my $good_guy = '$name is a good guy!' #if printed, outputs: $name is a good guy!

" … " (or qq//) #variable and backslash interpolation

my $hello = "hello\tsir!"; #if printed, outputs: hello sir

my $good_guy2 = "$name is a good guy!" #if printed, outputs: Vassilios is a good guy!

Double-quoted string escapes:Construct Meaning

\n newline

\r return

\t tab

\\ backslash

\" double quote \$, \@, \& etc…

VI, October 2006


#!/usr/bin/perl

use strict; use warnings;

my $pet_string = "This is to TEST\nsome string functions";

print $pet_string;

# lc returns lowercased version of $pet_string

my $lc_string = lc($pet_string);

print $lc_string;

# uc returns uppercased version of $pet_string

my $uc_string = uc($pet_string);

print $uc_string;

# length returns the length of $pet_string

my $length_string = length($pet_string);

print "$length_string";

print "*"x10;

print "\t".("*"x10)."\n";

exit;

Important strings functions I

This is to TEST

some string functions

this is to test

some string functions

THIS IS TO TEST

SOME STRING FUNCTIONS

38

********** **********



#!/usr/bin/perl

my $pet_string = "TEST of some\nstring functions\n";

print $pet_string;

# reverses $pet_string (character by character)

my $rev_string = reverse($pet_string);

print $rev_string."\n";

# takes 3 arguments: string value, zero-based

# initial position and length for the substring

my $sub_string = substr ($pet_string,0,15);

print $sub_string."\n";

# if a string ends in a newline character, chomp removes it

my $chomp_string = $pet_string;

print $chomp_string; chomp($chomp_string);

print $chomp_string;

# chop removes the last character of a string

my $chop_string = $chomp_string;

print $chop_string; chop($chop_string); print $chop_string;

exit;

Important strings functions II

TEST of some

string functions

snoitcnuf gnirts

emos fo TSET

TEST of some

TEST of some

string functions

TEST of some

string functions

TEST of some

string functionsTEST of some

string functionsTEST of some

string functionvioannid$

VI, October 2006

Perl variables - Arrays & Hashes

Multivalued Data Structures:

0 1 2 3

car bike van plane

@locomotion

%days

Mon

Monday

Tue

TuesdayWed

Wednesday

Thu

Thursday

Fri

Friday

Sat

Saturday

Sun

Sunday


Perl variables - Arrays

#!/usr/bin/perl

# array of strings

my @string_numbers = ('One', 'Two', 'Three', 'Four');

print @string_numbers;

print "\n";

# array of integers

my @numeric_numbers = (1..5);

print "@numeric_numbers\n";

my @numeric_numbers2 = (1,2,3,4,5);

print "@numeric_numbers2\n";

print "$string_numbers[2]\n";

exit;

arrays I

Normal arrays are ordered lists of scalars indexed by number (starting with 0).

Entire arrays are denoted by '@', which works much like the word "these" or "those" does in

English, in that it indicates multiple values are expected.

OneTwoThreeFour

1 2 3 4 5

1 2 3 4 5

Three

VI, October 2006


#!/usr/bin/perl

# array of strings

my @string_numbers = ('One', 'Two', 'Three', 'Four');

# replaces One with Zero in @string_numbers

$string_numbers[0] = 'Zero';

print "@string_numbers\n";

my @sort_string_numbers = sort @string_numbers;

print "@sort_string_numbers\n";

print scalar @string_numbers;

print "\n";

my $nb = @string_numbers;

print "$nb\n";

exit;

arrays II

Zero Two Three Four

Four Three Two Zero

4

4



#!/usr/bin/perl

my @string_numbers = ('Zero', 'Two', 'Three', 'Four');

my $end = $string_numbers[$#string_numbers];

print "$end\n";

# swap values

($gene1, $gene2) = ($gene2, $gene1);

# variable interpolation

my @login = ("$username", "$password");

my @anyarray = (6, "hello", @string_numbers );

my @rev_anyarray = reverse @rev_anyarray;

print "@anyarray\n";

print "@rev_anyarray\n";

exit;

arrays III

Four

6 hello Zero Two Three Four

Four Three Two Zero hello 6

VI, October 2006

Perl variables

Some arrays functions:

sort sorts all the elements of an array.

reverse inverses the order of all the elements of an array.

shift, unshift takes the first element, places an element at the first position of the array.

pop, push takes the last element, places an element at the last position of the array.

A B C D E F


Perl variables

ABCDEF






VI, October 2006

Perl variables

ABCDE

F

F







Perl variables

BCDEF

A

A






VI, October 2006

Perl variables - Arrays & Hashes

Multivalued Data Structures:

0 1 2 3

car bike van plane

@locomotion

%days

Mon

Monday

Tue

TuesdayWed

Wednesday

Thu

Thursday

Fri

Friday

Sat

Saturday

Sun

Sunday


Perl variables

hashes (associative arrays of scalars)

Hashes are unordered collections of scalar values indexed by their associated string key.

Entire hashes are denoted by '%'

TyrTAT

CysTGT

SerTCT

PheTTT

ValueKey%days

Mon

Monday

Tue

TuesdayWed

Wednesday

Thu

Thursday

Fri

Friday

Sat

Saturday

Sun

Sunday

#!/usr/bin/perl

my %codon3 = (

"TTT" => "Phe",

"TTA" => "Leu",

);

print $codon3{'TTT'};

print "\n";

exit;

vioannid$ ./hash.pl

Phe

vioannid$

VI, October 2006

Perl variables

hashes (associative arrays of scalars)

Hashes are unordered collections of scalar values indexed by their associated string key.

Entire hashes are denoted by '%'

- a hash is preferably used when we want to search for something with a "name" (string)

- a hash is preferably used when we do not care what order the items are in (or easy to sort)

- a hash has no beginning or end

- hashes are very fast scalar lookup structures

- key: the string value index (must be unique!)

- value: the scalar value accessed by the key

- hash key string values cannot be altered.

(one has to insert a new key with the value from the old key and then delete the old key)


Perl variables

hashes I

#!/usr/bin/perl

my %some_hash = ("John", "Travolta", "Betty", "Bossy");

print $some_hash{"John"}."\n";

my %capitals = (

'china' => 'beijing',

'france' => 'paris',

'italy' => 'rome',

'switzerland' => 'bern',

);

print %capitals;

print "\n";

print $capitals{'china'}."\n";

my @k = keys %capitals;

my @v = values %capitals;

print "@k\n";

print "@v\n";

exit;

Travolta

switzerlandbernitalyromefranceparischinabeijing

beijing

switzerland italy france china

bern rome paris beijing

VI, October 2006

Perl variables

hashes II

#!/usr/bin/perl

my %capitals = (

'china' => 'beijing',

'france' => 'paris',

'italy' => 'rome',

'switzerland' => 'bern',

);

my $nb = keys %capitals;

print "$nb\n";

my %rev_capitals = reverse %capitals;

print %rev_capitals;

print "\n";

print $rev_capitals{'china'}."\n";

print $rev_capitals{'beijing'}."\n";

exit;

4

beijingchinabernswitzerlandparisfranceromeitaly

china


Perl - Getting User Input

How to get a value from the keyboard into a Perl program ?

The simplest way is to use the line-input operator: <STDIN>

Each time we use <STDIN> in a place where a scalar value is expected, Perl reads the next complete

text line up to the first newline from the keyboard (unless you modified it).

#!/usr/bin/perl

print "Please enter your Lastname: ";

my $lastname = <STDIN>;

print "Please enter your Firstname: ";

my $firstname = <STDIN>;

print "Hello $firstname $lastname,\n

I hope you like Perl programming !\n";

exit;

Please enter your Lastname:

Please enter your Firstname: Vassilios

Ioannidis

Hello Vassilios

Ioannidis

,

I hope you like Perl programming !

VI, October 2006

Perl - Getting User Input

How to get a value from the keyboard into a Perl program ?

The simplest way is to use the line-input operator: <STDIN>

Each time we use <STDIN> in a place where a scalar value is expected, Perl reads the next complete

text line up to the first newline from the keyboard (unless you modified it).

Please enter your Lastname:

Please enter your Firstname: Vassilios

Ioannidis

Hello Vassilios Ioannidis,

I hope you like Perl programming !

#!/usr/bin/perl

print "Please enter your Lastname: ";

my $lastname = <STDIN>;

chomp $lastname;

print "Please enter your Firstname: ";

my $firstname = <STDIN>;

chomp $firstname;

print "Hello $firstname $lastname,\n

I hope you like Perl programming !\n";

exit;


Perl operators

Perl operators

Arithmetic+ addition

- subtraction

* multiplication

/ division

Numeric comparison

== equality!= inequality

< less than

> greater than

<= less than or equal

>= greater than or equal

String comparisoneq equality

ne inequality

lt less than

gt greater than

le less than or equal

ge greater than or equal

Why do we have separate numeric and string comparisons?

Because we don't have special variable types, and Perl needs to know whether to sort

numerically (where 99 is less than 100) or alphabetically (where 100 comes before 99).

VI, October 2006

Perl operators

Perl operators


use strict;

use warnings;

my $x = 100;

my $y = 99;

if ($x > $y) { print "\"$x\" is numerically greater than \"$y\"\n" ; }

else { print "\"$x\" is numerically smaller than \"$y\"\n" ; }

if ($x gt $y) { print "\"$x\" is alphabetically greater than \"$y\"\n" ; }

else { print "\"$x\" is alphabetically smaller than \"$y\"\n" ; }

exit ;

vioannid$ ./string_num_comp.pl

"100" is numerically greater than "99"

"100" is alphabetically smaller than "99"

vioannid$


Perl operators

Perl operators

Boolean logic&& and

|| or

! not

Miscellaneous= assignment

. string concatenation

x string multiplication

.. range operator (creates a list of numbers)

Many operators can be combined with a "=" as follows:

$a += 1; # same as $a = $a + 1; #same as $a++;

$a -= 1; # same as $a = $a - 1; #same as $a--;

$a .= "\n"; # same as $a = $a. "\n";

VI, October 2006

Perl statement modifiers

Any simple statement may optionally be followed by a SINGLE modifier, just before the terminating

semicolon (or block ending). The possible modifiers are:

if (EXPR) { }

unless (EXPR) { }

foreach (LIST ) { }

while (EXPR ) { }

until (EXPR ) { }

The EXPR following the modifier is referred to as the "condition". Its truth or falsehood determines

how the modifier will behave.

if executes the statement once if and only if the condition is true .

unless is the opposite, it executes the statement if the condition is false (unless the condition is true).

The foreach modifier is an iterator: it executes the statement once for each item in the LIST (with $_

aliased to each item in turn).

while repeats the statement while the condition is true.

until does the opposite, it repeats the statement until the condition is true (or while the condition is

false): The while and until modifiers have the usual "while loop" semantics (conditional

evaluated first).



if / if else / if elsif else

#!/usr/bin/perl

use strict;

use warnings;

print "\nEnter your name (then press \"return\" when done):\t";

#get information from the terminal window

my $name = <STDIN>;

#remove trailing "\n" if any

chomp $name;

if ($name eq "Couchepin") { print "Hello Mr President !\n" ; }

exit ;

VI, October 2006



#!/usr/bin/perl

use strict;

use warnings;



my $name = <STDIN>;


chomp $name;


else { print "Hello $name !\n" ; }

exit ;




#!/usr/bin/perl

use strict;

use warnings;



my $name = <STDIN>;


chomp $name;


elsif ($name eq "Falquet") { print "Good day to you Master $name !\n" ; }

else { print "Hello $name !\n" ; }

exit ;

VI, October 2006


Perl looping the for/foreach loop:

"Passing an array":foreach my $element ( @array ) {

# do something with the element

}

"Passing a hash":foreach my $key (keys %hash) {

print "The value of $key is $hash{$key}\n";

}

"specify 3 EXPR inside the (): initial state, condition and loop expression":

for ($i = 0; $i <= 10; $i=$i+1 ) {

#execute the contents of the block as long as $i is less than, or equal to 10 or while $i is smaller than 10.

}




#!/usr/bin/perl

use strict;

use warnings;

my $counter;

for ($counter=1;$counter<=10;$counter++) {

print "I can count up to $counter !\n";

}

exit ;

I can count up to 1 !










VI, October 2006



#!/usr/bin/perl

use strict;

use warnings;

my @names = (

"Simon","Arnaud","Todd","Natacha",

"Francesca","Jan","Jeremy","Claudia",

"Magdalena","Marcel","James","Joachim",

"Sutada","Mingkwan","sivaraman","Ralf",

"Kurt","Liviu","Dinesh","Eleonore", "Paul","Fekadu"

);

foreach my $name (@names) {

print "Hello $name !\n";

}

exit ;

vioannid$ ./list_fname.pl

Hello Simon !

Hello Arnaud !

Hello Todd !

Hello Natacha !

Hello Francesca !

Hello Jan !

Hello Jeremy !

Hello Claudia !

Hello Magdalena !

Hello Marcel !

Hello James !

Hello Joachim !

Hello Sutada !

Hello Mingkwan !

Hello sivaraman !

Hello Ralf !

Hello Kurt !

Hello Liviu !

Hello Dinesh !

Hello Eleonore !

Hello Paul !

Hello Fekadu !

vioannid$




#!/usr/bin/perl

use strict;

use warnings;

my @names = (

"Simon","Arnaud","Todd","Natacha",

"Francesca","Jan","Jeremy","Claudia",

"Magdalena","Marcel","James","Joachim",

"Sutada","Mingkwan","sivaraman","Ralf",

"Kurt","Liviu","Dinesh","Eleonore", "Paul","Fekadu"

);

foreach (sort @names) {

print "Hello $_ !\n";

}

exit ;

vioannid$ ./list_fname.pl

Hello Arnaud !

Hello Claudia !

Hello Dinesh !

Hello Eleonore !

Hello Fekadu !

Hello Francesca !

Hello James !

Hello Jan !

Hello Jeremy !

Hello Joachim !

Hello Kurt !

Hello Liviu !

Hello Magdalena !

Hello Marcel !

Hello Mingkwan !

Hello Natacha !

Hello Paul !

Hello Ralf !

Hello Simon !

Hello Sutada !

Hello Todd !

Hello sivaraman !

vioannid$

VI, October 2006

Perl special variables (small extract)

$_ The default input and pattern searching space.

$& The string matched by the last successful pattern match.

$` The string preceding whatever was matched by the last successful pattern match.

$' The string following whatever was matched by the last successful pattern match.

$! If a system or library call fails, it sets this variable This means that the value of $! is

meaningful only immediately after a failure.

$/ The input record separator, newline by default .

$$ The process number of the Perl running this script.

@ARGV commandline arguments (space separation by default).

note:

$ARGV[0] first commandline argument …




#!/usr/bin/perl

use strict; use warnings;

my %names = (

"Barkow"=>"Simon", "Basle"=>"Arnaud",

"Blevins"=>"Todd", "Bodenhausen"=>"Natacha",

"Botta"=>"Francesca", "Kerschgens"=>"Jan",

"Keusch"=>"Jeremy", "Kutter"=>"Claudia",

"Livingstone"=>"Magdalena", "Meury"=>"Marcel",

"Moore"=>"James", "Muller"=>"Joachim",

"Mungpakdee"=>"Sutada",

"Nipitwattanaphon"=>"Mingkwan",

"Padavattan"=>"sivaraman", "Paul"=>"Ralf",

"Tobler"=>"Kurt", "Vanoaica"=>"Liviu", "Vellore

Palanivelu"=>"Dinesh", "Wassmann"=>"Paul",

"Yadetie"=>"Fekadu", "von Castelmur"=>"Eleonore",

);

foreach my $key (sort keys %names) {

print "The firstname of $key is $names{$key}\n";

}

exit ;

vioannid$ ./list_fname_hash.pl

The firstname of Barkow is Simon

The firstname of Basle is Arnaud

The firstname of Blevins is Todd

The firstname of Bodenhausen is Natacha

The firstname of Botta is Francesca

The firstname of Kerschgens is Jan

The firstname of Keusch is Jeremy

The firstname of Kutter is Claudia

The firstname of Livingstone is Magdalena

The firstname of Meury is Marcel

The firstname of Moore is James

The firstname of Muller is Joachim

The firstname of Mungpakdee is Sutada

The firstname of Nipitwattanaphon is Mingkwan

The firstname of Padavattan is sivaraman

The firstname of Paul is Ralf

The firstname of Tobler is Kurt

The firstname of Vanoaica is Liviu

The firstname of Vellore Palanivelu is Dinesh

The firstname of Wassmann is Paul

The firstname of Yadetie is Fekadu

The firstname of von Castelmur is Eleonore

vioannid$

VI, October 2006


Perl looping the while loop

while ( condition ) {

#execute the contents of the block

}

Warning: Infinite Loop !!!

while (1) {

#execute the contents of the block forever !

}

True/False

In Perl some variables are considered true:

- integer with a nonzero value

- string with nonzero length

- array with at least one element

- hash with at least one key/value pair

For example:

$lang = "Perl"; # < true

$version = 5.6; # < true

$zero = 0; # < false

$empty = ""; # < false

@states = (); # < false

%table = (1 => "one"); # < true


#!/usr/bin/perl

use strict;

use warnings;

my $number = 1;

while ($number<=10) {

print "I can count up to $number !";

$number+=1; #Ha !

}

exit ;



#!/usr/bin/perl

use strict;

use warnings;

my $number = 1;



}

exit ; #really ? Tip:

To stop a "looping" script press CTRL+C …

















^C

vioannid$

VI, October 2006

#!/usr/bin/perl

use strict;

use warnings;

my $number = 1;



$number+=1; #Ha !

}

exit ;



#!/usr/bin/perl

use strict;

use warnings;

my $number = 1;



$number = $number+1;

#same as $number += 1;

#same as $number++;

}

exit ;

vioannid$ ./list_while_array.pl











vioannid$


Perl Documents, help, debugging

perl -h

perldoc <keyword>

Web help

www.perl.org

www.perl.com

Books

O’Reilly

www.oreilly.com

Debugging?

use strict;

use warnings;

"abuse" of the print !

./script.pl -d

(debug mode)

man perldebug

VI, October 2006

Perl