Perl - Introduction & Quick Guide

Perl - Quick Guide

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Perl - Introduction

Perl is a general-purpose programming language originally developed for text manipulation and now used for a wide range of tasks including system administration, web development, network programming, GUI development, and more.

What is Perl?

·        Perl is a stable, cross platform programming language.

·        Though Perl is not officially an acronym but few people used it as Practical Extraction and Report Language.

·        It is used for mission critical projects in the public and private sectors.

·        Perl is an Open Source software, licensed under its Artistic License, or the GNU General Public License (GPL).

·        Perl was created by Larry Wall.

·        Perl 1.0 was released to usenet's alt.comp.sources in 1987

·        At the time of writing thi tutorial, latest version of perl is 5.16.2

·        Perl is listed in the Oxford English Dictionary.

PC Magazine named Perl a finalist for its 1998 Technical Excellence Award in the Development Tool category.

Perl Features

·        Perl takes the best features from other languages, such as C, awk, sed, sh, and BASIC, among others.

·        Perls database integration interface DBI supports third-party databases including Oracle, Sybase, Postgres, MySQL and others.

·        Perl works with HTML, XML, and other mark-up languages.

·        Perl supports Unicode.

·        Perl is Y2K compliant.

·        Perl supports both procedural and object-oriented programming.

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

·        Perl is extensible. There are over 20,000 third party modules available from the Comprehensive Perl Archive Network (CPAN).

·        The Perl interpreter can be embedded into other systems.

Perl and the Web

·        Perl used to be the most popular web programming language due to its text manipulation capabilities and rapid development cycle.

·        Perl is widely known as " the duct-tape of the Internet".

·        Perl can handle encrypted Web data, including e-commerce transactions.

·        Perl can be embedded into web servers to speed up processing by as much as 2000%.

·        Perl's mod_perl allows the Apache web server to embed a Perl interpreter.

• Perl's DBI package makes web-database integration easy.

Perl is Interpreted

Perl is an interpreted, which means that your code can be run as is, without a compilation stage that creates a non portable executable program.

Traditional compilers convert programs into machine language. When you run a Perl program, it's first compiled into a byte code, which is then converted ( as the program runs) into machine instructions. So it is not quite the same as shells, or Tcl, which are strictlyinterpreted without an intermediate representation.

Neither it is like most versions of C or C++, which are compiled directly into a machine dependent format. It is somewhere in between, along with Python and awk and Emacs .elc files.

Perl - Environment Setup

Before we start writing our Perl programs, let's understand how to setup our Perl environment. Perl is available on a wide variety of platforms:

·        Unix (Solaris, Linux, FreeBSD, AIX, HP/UX, SunOS, IRIX etc.)

·        Win 9x/NT/2000/

·        WinCE

·        Macintosh (PPC, 68K)

·        Solaris (x86, SPARC)

·        OpenVMS

·        Alpha (7.2 and later)

·        Symbian

·        Debian GNU/kFreeBSD

·        MirOS BSD

·        And many more...

This is more likely that your system will have perl installed on it. Just try giving following command at the $ prompt:

$perl -v

If you have perl installed on your machine then you will get a message something as follows:

This is perl 5, version 16, subversion 2 (v5.16.2) built for i686-linux

Copyright 1987-2012, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the

GNU General Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on

this system using "man perl" or "perldoc perl".  If you have access to the

Internet, point your browser at http://www.perl.org/, the Perl Home Page.

If you do not have perl already installed then proceed to the next section.

Getting Perl Installation

The most up-to-date and current source code, binaries, documentation, news, etc. is available at the official website of Perl:

Perl Official Website : http://www.perl.org/

You can download Perl documentation from the following site.

Perl Documentation Website : http://perldoc.perl.org

Install Perl:

Perl distribution is available for a wide variety of platforms. You need to download only the binary code applicable for your platform and install Perl.

If the binary code for your platform is not available, you need a C compiler to compile the source code manually. Compiling the source code offers more flexibility in terms of choice of features that you require in your installation.

Here is a quick overview of installing Perl on various platforms:

Unix & Linux Installation

Here are the simple steps to install Perl on Unix/Linux machine.

·        Open a Web browser and go to http://www.perl.org/get.html

·        Follow the link to download zipped source code available for Unix/Linux.

·        Download perl-5.x.y.tar.gz file and issue the following commands at $ prompt.

$tar -xzf perl-5.x.y.tar.gz

$cd perl-5.x.y

$./Configure -de

$make

$make test

$make install

NOTE: Here $ is Unix prompt where you type your command, so make sure you are not typing $ while typing above mentioned commands.

This will install Perl in a standard location /usr/local/bin and its libraries are installed in/usr/local/lib/perlXX where XX is the version of Perl that you are using.

It will take a while to compile the source code after issuing make command. Once installation is done, you can issue perl -v command at $ prompt to check perl installation. If everything is fine then it will display message like I have shown above.

Windows Installation:

Here are the steps to install Perl on Windows machine.

·        Follow the link for the Strawberry Perl installation on Windowshttp://strawberryperl.com

·        Download either 32bit or 64bit version of installation.

·        Run the downloaded file by double-clicking it in Windows Explorer. This brings up the Perl install wizard, which is really easy to use. Just accept the default settings, wait until the install is finished, and you're ready to roll!

Macintosh Installation

In order to build your own version of Perl you will need 'make' this is part of the Apples developer tools usually supplied with Mac OS install DVDs. You do not need the latest version of Xcode (which is now charged for) in order to install make.

Here are the simple steps to install Perl on Mac OS X machine.

·        Open a Web browser and go to http://www.perl.org/get.html

·        Follow the link to download zipped source code available for Mac OS X.

·        Download perl-5.x.y.tar.gz file and issue the following commands at $ prompt.

$tar -xzf perl-5.x.y.tar.gz

$cd perl-5.x.y

$./Configure -de

$make

$make test

$make install

This will install Perl in a standard location /usr/local/bin and its libraries are installed in/usr/local/lib/perlXX where XX is the version of Perl that you are using.

Running Perl

There are following different ways to start Perl:

(1) Interactive Interpreter:

You can enter perl and start coding right away in the interactive interpreter by starting it from the command line. You can do this from Unix, DOS, or any other system which provides you a command-line interpreter or shell window.

$perl  -e <perl code>           # Unix/Linux

or

C:>perl -e <perl code>          # Windows/DOS

Here is the list of all the available command line options:

Option	Description
-d[:debugger]	Run program under debugger
-Idirectory	Specify @INC/#include directory
-T	Enable tainting checks
-t	Enable tainting warnings
-U	Allow unsafe operations
-w	Enable many useful warnings
-W	Enable all warnings
-X	Disable all warnings
-e program	run Perl script sent in as program
file	run Perl script from a given file

(2) Script from the Command-line:

A Perl script is a text file which keeps perl code in it and it can be executed at command line by invoking the interpreter on your application, as in the following:

$perl  script.pl          # Unix/Linux

or

C:>perl script.pl         # Windows/DOS

(3) Integrated Development Environment

You can run Perl from a graphical user interface (GUI) environment as well. All you need is a GUI application on your system that supports Perl. You can download Padre, the Perl IDE. You can also use Eclipse Plugin EPIC - Perl Editor and IDE for Eclipse if you are familiar with Eclipse.

Before proceeding to next chapter, make sure your environment is properly setup and working perfectly fine. If you are not able to setup the environment properly then you can take help from your system admininstrator.

Al the examples given in subsequent chapters have been executed with v5.16.2 version available on CentOS flavor of Linux.

Perl - Syntax Overview

Perl borrows syntax and concepts from many languages: awk, sed, C, Bourne Shell, Smalltalk, Lisp and even English. However, there are some definite differences between the languages. This chapter is designed to quickly get you up to speed on the syntax that is expected in Perl.

A Perl program consists of a sequence of declarations and statements which run from the top to the bottom. Loops, subroutines, and other control structures allow you to jump around within the code. Every simple statement must end with a semicolon (;).

Perl is a free-form language: you can format and indent it however you like. Whitespace serves mostly to separate tokens, unlike languages like Python where it is an important part of the syntax, or Fortran where it is immaterial.

First Perl Program

Interactive Mode Programming:

You can use Perl interpreter with -e option at command line which lets you execute Perl statements from the command line. Let's try something at $ prompt as follows:

$perl -e 'print "Hello World\n"'

This execution will produce following result:

Hello, world

Script Mode Programming

Assuming you are already on $ prompt. So let's open a text file hello.pl using vi or vim editor and put the following lines inside your file.

#!/usr/bin/perl

# This will print "Hello, World"

print "Hello, world\n";

Here /usr/bin/perl is actual perl interpreter binary. Before you execute your script be sure to change the mode of the script file and give execution priviledge, generally a setting of 0755 works perfectly and finally and finally you execute above script as follows:

$chmod 0755 hello.pl

$./hello.pl

This execution will produce following result:

Hello, world

You can use parentheses for functions arguments or omit them according to your personal taste. They are only required occasionally to clarify issues of precedence. Following two statements produce same result.

print("Hello, world\n");

print "Hello, world\n";

Perl File Extension

A Perl script can be created inside of any normal simple-text editor program. There are several programs available for every type of platform. There are many programs designed for programmers available for download on the web.

As a Perl convention, a Perl file must be saved with a .pl or .PL file extension in order to be recognized as a functioning Perl script. File names can contain numbers, symbols, and letters but must not contain a space. Use an underscore (_) in places of spaces.

Comments in Perl

Comments in any programming language are friends of developers. Comments can be used to make program user friendly and they are simply skipped by the interpreter without impacting code functionality. For example, in the above program a line starting with hash #is a comment.

Simply saying comments in Perl start with a hash symbol and run to the end of the line:

# This is a comment in perl

Lines starting with = are interpreted as the start of a section of embedded documentation (pod), and all subsequent lines until the next =cut are ignored by the compiler. Following is the example:

#!/usr/bin/perl

# This is a single line comment

print "Hello, world\n";

=begin comment

This is all part of multiline comment.

You can use as many lines as you like

These comments will be ignored by the

compiler until the next =cut is encountered.

=cut

This will produce following result:

Hello, world

Whitespaces in Perl

A Perl program does not care about whitespaces. Following program works perfectly fine:

#!/usr/bin/perl

print       "Hello, world\n";

But if spaces are inside the quoted strings then they would be printed as is. For example:

#!/usr/bin/perl

# This would print with a line break in the middle

print "Hello

between the << and the identifier.

An identifier may be either a bare word or some quoted text like we used EOF below. If identifier is quoted, the type of quote you use determines the treatment of the text inside the here docoment, just as in regular quoting. An unquoted identifier works like double quotes.

#!/usr/bin/perl

$a = 10;

$var = <<"EOF";

This is the syntax for here document and it will continue

until it encounters a EOF in the first line.

This is case of double quote so variable value will be

interpolated. For example value of a = $a

EOF

print "$var\n";

$var = <<'EOF';

This is case of single quote so variable value will not be

interpolated. For example value of a = $a

EOF

print "$var\n";

This will produce following result:

This is the syntax for here document and it will continue

until it encounters a EOF in the first line.

This is case of double quote so variable value will be

interpolated. For example value of a = 10

This is case of single quote so variable value will be

interpolated. For example value of a = $a

Escaping Characters

Perl uses the backslash (\) character to escape any type of character that might interfere with our code. Let's take one example where we want to print double quote and $ sign:

#!/usr/bin/perl

$result = "This is \"number\"";

print "$result\n";

print "\$result\n";

This will produce following result:

This is "number"

$result

Perl Identifiers:

A Perl identifier is a name used to identify a variable, function, class, module, or other object. A Perl variable name starts with either $, @ or % followed by zero or more letters, underscores, and digits (0 to 9).

Perl does not allow punctuation characters such as @, $, and % within identifiers. Perl is acase sensitive programming language. Thus $Manpower and $manpower are two different identifiers in Perl.

Perl - Data Types

Perl is loosely typed language and there is no need to specify a type for your data while using in your program. The Perl interpreter will choose the type based on the context of the data itself.

Perl has three basic data types: scalars, arrays of scalars, and hashes of scalars, also known as associative arrays. Here is little detail about these data types.

S.N.	Types and Description
1	Scalar: Scalars are simple variables. They are preceded by a dollar sign ($). A scalar is either a number, a string, or a reference. A reference is actually an address of a variable which we will see in upcoming chapters.
2	Arrays: Arrays are ordered lists of scalars that you access with a numeric index which starts with 0. They are preceded by an "at" sign (@).
3	Hashes: Hashes are unordered sets of key/value pairs that you access using the keys as subscripts. They are preceded by a percent sign (%).

Numeric Literals

Perl stores all the numbers internally as either signed integers or double-precision floating-point values. Numeric literals are specified in any of the following floating-point or integer formats:

Type	Value
Integer	1234
Negative integer	-100
Floating point	2000
Scientific notation	16.12E14
Hexadecimal	0xffff
Octal	0577

String Literals

Strings are sequences of characters. They are usually alphanumeric values delimited by either single (') or double (") quotes. They work much like UNIX shell quotes where you can use single quoted strings and double quoted strings.

Double-quoted string literals allows variable interpolation, and single-quoted strings are not. There are certain characters when they are proceeded by a back slash they will have special meaning and they are used to represent like newline (\n) or tab (\t).

You can embed newlines or any of the following Escape sequences directly in your double quoted strings:

Escape sequence	Meaning
\\	Backslash
\'	Single quote
\"	Double quote
\a	Alert or bell
\b	Backspace
\f	Form feed
\n	Newline
\r	Carriage return
\t	Horizontal tab
\v	Vertical tab
\0nn	Creates Octal formatted numbers
\xnn	Creates Hexideciamal formatted numbers
\cX	Control characters, x may be any character
\u	Force next character to uppercase
\l	Force next character to lowercase
\U	Force all following characters to uppercase
\L	Force all following characters to lowercase
\Q	Backslash all following non-alphanumeric characters
\E	End \U, \L, or \Q

Example

Let's see again how strings behaves with single quotation and double quotation. Here we will use string escapes mentioned in the above table and will make use of scalar variable to assign string values.

#!/usr/bin/perl

# This is case of interpolation.

$str = "Welcome to \ntutorialspoint.com!";

print "$str\n";

# This is case of non-interpolation.

$str = 'Welcome to \ntutorialspoint.com!';

print "$str\n";

# Only W will become upper case.

$str = "\uwelcome to tutorialspoint.com!";

print "$str\n";

# Whole line will become capital.

$str = "\UWelcome to tutorialspoint.com!";

print "$str\n";

# A portion of line will become capital.

$str = "Welcome to \Ututorialspoint\E.com!";

print "$str\n";

# Backsalash non alpha-numeric including spaces.

$str = "\QWelcome to tutorialspoint's family";

print "$str\n";

This will produce following result:

Welcome to

tutorialspoint.com!

Welcome to \ntutorialspoint.com!

Welcome to tutorialspoint.com!

WELCOME TO TUTORIALSPOINT.COM!

Welcome to TUTORIALSPOINT.com!

Welcome\ to\ tutorialspoint\'s\ family

Perl - Variables

Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory.

Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals, or strings in these variables.

We have learnt that Perl has following three basic data types:

·        Scalars

·        Arrays

·        Hashes

Accordingly we are going to use three types of variables in Perl. A scalar variable will precede by a dollar sign ($) and it can store either a number, a string, or a reference. Aarray variable will precede by sign @ and it will store ordered lists of scalars. Finaly Hashvariable will precede by sign % and will be used to store sets of key/value pairs.

Perl maintains every variable type in a separate namespace. So you can, without fear of conflict, use the same name for a scalar variable, an array, or a hash. This means that $foo and @foo are two different variables.

Creating Variables

Perl variables do not have to be explicitly declared to reserve memory space. The declaration happens automatically when you assign a value to a variable. The equal sign (=) is used to assign values to variables.

Keep a note that this is mandatory to declare a varibale before we use it if we use use strict statement in our program.

The operand to the left of the = operator is the name of the variable, and the operand to the right of the = operator is the value stored in the variable. For example:

$age = 25;             # An integer assignment

$name = "John Paul";   # A string

$salary = 1445.50;     # A floating point

Here 25, "John Paul" and 1445.50 are the values assigned to $age, $name and $salaryvariables, respectively. Shortly we will see how we can assign values to arrays and hashes.

Scalar Variables

A scalar is a single unit of data. That data might be a integer number, floating point, a character, a string, a paragraph, or an entire web page. Simply saying it could be anything, but only a single thing.

Here is a simple example of using scalar variables:

#!/usr/bin/perl

$age = 25;             # An integer assignment

$name = "John Paul";   # A string

$salary = 1445.50;     # A floating point

print "Age = $age\n";

print "Name = $name\n";

print "Salary = $salary\n";

This will produce following result:

Age = 25

Name = John Paul

Salary = 1445.5

Array Variables

An array is a variable that stores an ordered list of scalar values. Array variables are preceded by an "at" (@) sign. To refer to a single element of an array, you will use the dollar sign ($) with the variable name followed by the index of the element in square brackets.

Here is a simple example of using array variables:

#!/usr/bin/perl

@ages = (25, 30, 40);            

@names = ("John Paul", "Lisa", "Kumar");

print "\$ages[0] = $ages[0]\n";

print "\$ages[1] = $ages[1]\n";

print "\$ages[2] = $ages[2]\n";

print "\$names[0] = $names[0]\n";

print "\$names[1] = $names[1]\n";

print "\$names[2] = $names[2]\n";

Here we used escape sign (\) before $ sign just to print it other Perl will understand it as a variable and will print its value. When exected, this will produce following result:

$ages[0] = 25

$ages[1] = 30

$ages[2] = 40

$names[0] = John Paul

$names[1] = Lisa

$names[2] = Kumar

Hash Variables

A hash is a set of key/value pairs. Hash variables are preceded by a percent (%) sign. To refer to a single element of a hash, you will use the hash variable name followed by the "key" associated with the value in curly brackets.

Here is a simple example of using hash variables:

#!/usr/bin/perl

%data = ('John Paul', 45, 'Lisa', 30, 'Kumar', 40);

print "\$data{'John Paul'} = $data{'John Paul'}\n";

print "\$data{'Lisa'} = $data{'Lisa'}\n";

print "\$data{'Kumar'} = $data{'Kumar'}\n";

This will produce following result:

$data{'John Paul'} = 45

$data{'Lisa'} = 30

$data{'Kumar'} = 40

Variable Context

Perl treats same variable differently based on Context ie. situation where a variable is being used. Let's check following example:

#!/usr/bin/perl

@names = ('John Paul', 'Lisa', 'Kumar');

@copy = @names;

$size = @names;

print "Given names are : @copy\n";

print "Number of names are : $size\n";

This will produce following result:

Given names are : John Paul Lisa Kumar

Number of names are : 3

Here @names is an array, which has been used in two different contexts. First we copied it into anyother array ie. list so it returned all the elements assuming that context is list context. Next we used same array and tried to store this array in a scalar, so in this case it returned just number of elements in this array assuming that context is scalar context. Following table lists down various contexts:

S.N.	Context and Description
1	Scalar: Assignment to a scalar variable evaluates the right-hand side in a scalar context.
2	List: Assignment to an array or a hash evaluates the right-hand side in a list context.
3	Boolean: Boolean context is simply any place where an expression is being evaluated to see whether it's true or false.
4	Void: This context not only doesn't care what the return value is, it doesn't even want a return value.
5	Interpolative: This context only happens inside quotes, or things that work like quotes.

Perl - Scalers

A scalar is a single unit of data. That data might be a integer number, floating point, a character, a string, a paragraph, or an entire web page. Simply saying it could be anything, but only a single thing.

Here is a simple example of using scalar variables:

#!/usr/bin/perl

$age = 25;             # An integer assignment

$name = "John Paul";   # A string

$salary = 1445.50;     # A floating point

print "Age = $age\n";

print "Name = $name\n";

print "Salary = $salary\n";

This will produce following result:

Age = 25

Name = John Paul

Salary = 1445.5

Numeric Scalars

A scalar is most often either a number or a string. Following example demonstrates the usage of various types of numeric scalars:

#!/usr/bin/perl

$integer = 200;

$negative = -300;

$floating = 200.340;

$bigfloat = -1.2E-23;

# 377 octal, same as 255 decimal

$octal = 0377;

# FF hex, also 255 decimal

$hexa = 0xff;

print "integer = $integer\n";

print "negative = $negative\n";

print "floating = $floating\n";

print "bigfloat = $bigfloat\n";

print "octal = $octal\n";

print "hexa = $hexa\n";

This will produce following result:

integer = 200

negative = -300

floating = 200.34

bigfloat = -1.2e-23

octal = 255

hexa = 255

String Scalars

Following example demonstrates the usage of various types of string scalars. Notice the difference between single quoted strings and double quoted strings:

#!/usr/bin/perl

$var = "This is string scalar!";

$quote = 'I m inside single quote - $var';

$double = "This is inside single quote - $var";

$escape = "This example of escape -\tHello, World!";

print "var = $var\n";

print "quote = $quote\n";

print "double = $double\n";

print "escape = $escape\n";

This will produce following result:

var = This is string scalar!

quote = I m inside single quote - $var

double = This is inside single quote - This is string scalar!

escape = This example of escape - Hello, World!

Scalar Operations

You will see a detail of various operators available in Perl in a separate chapter but here I'm going to list down few numeric and string operations.

#!/usr/bin/perl

$str = "hello" . "world";       # Concatenates strings.

$num = 5 + 10;                  # adds two numbers.

$mul = 4 * 5;                   # multiplies two numbers.

$mix = $str . $num;             # concatenates string and number.

print "str = $str\n";

print "num = $num\n";

print "mix = $mix\n";

This will produce following result:

str = helloworld

num = 15

mix = helloworld15

Multiline Strings

If you want to introduce multiline strings into your programs, you can use standard single quotes as below:

#!/usr/bin/perl

$string = 'This is

a multiline

string';

print "$string\n";

This will produce following result:

This is

a multiline

string

You can use "here" document syntax as well to store or print multilines as below:

#!/usr/bin/perl

print <<EOF;

This is

a multiline

string

EOF

This will also produce the same result:

This is

a multiline

string

V-Strings

A literal of the form v1.20.300.4000 is parsed as a string composed of characters with the specified ordinals. This form, known as v-strings.

A v-string provides an alternative and more readable way to construct strings, rather than use the somewhat less readable interpolation form "\x{1}\x{14}\x{12c}\x{fa0}".

They are any literal that begins with a v and is followed by one or more dot-separated elements. For example:

#!/usr/bin/perl

$smile  = v9786;

$foo    = v102.111.111;

$martin = v77.97.114.116.105.110;

print "smile = $smile\n";

print "foo = $foo\n";

print "martin = $martin\n";

This will also produce the same result:

smile = a?o

foo = foo

martin = Martin

Wide character in print at /tmp/135911788320439.pl line 7.

Special Literals

So far you must have a feeling about string scalars and its concatenation and interpolation opration. So let me tell you about three special literals __FILE__, __LINE__, and __PACKAGE__ represent the current filename, line number, and package name at that point in your program.

They may be used only as separate tokens and will not be interpolated into strings. Check below example:

#!/usr/bin/perl

print "File name ". __FILE__ . "\n";

print "Line Number " . __LINE__ ."\n";

print "Package " . __PACKAGE__ ."\n";

# they can not be interpolated

print "__FILE__ __LINE__ __PACKAGE__\n";

This will produce following result:

File name hello.pl

Line Number 4

Package main

__FILE__ __LINE__ __PACKAGE__

Perl - Arrays

An array is a variable that stores an ordered list of scalar values. Array variables are preceded by an "at" (@) sign. To refer to a single element of an array, you will use the dollar sign ($) with the variable name followed by the index of the element in square brackets.

Here is a simple example of using array variables:

#!/usr/bin/perl

@ages = (25, 30, 40);            

@names = ("John Paul", "Lisa", "Kumar");

print "\$ages[0] = $ages[0]\n";

print "\$ages[1] = $ages[1]\n";

print "\$ages[2] = $ages[2]\n";

print "\$names[0] = $names[0]\n";

print "\$names[1] = $names[1]\n";

print "\$names[2] = $names[2]\n";

Here we used escape sign (\) before $ sign just to print it other Perl will understand it as a variable and will print its value. When exected, this will produce following result:

$ages[0] = 25

$ages[1] = 30

$ages[2] = 40

$names[0] = John Paul

$names[1] = Lisa

$names[2] = Kumar

In Perl, List and Array terms are often used as if they're interchangeable. But the list is the data, and the array is the variable.

Array Creation

Array variables are prefixed with the @ sign and are populated using either parentheses or the qw operator. For example:

@array = (1, 2, 'Hello');

@array = qw/This is an array/;

The second line uses the qw// operator, which returns a list of strings, separating the delimited string by white space. In this example, this leads to a four-element array; the first element is 'this' and last (fourth) is 'array'. This means that you can use different lines as follows:

@days = qw/Monday

Tuesday

...

Sunday/;

You can also populate an array by assigning each value individually as follows:

$array[0] = 'Monday';

...

$array[6] = 'Sunday';

Accessing Array Elements

When accessing individual elements from an array, you must prefix the variable with a dollar sign ($) and then append the element index within square brackets after the name of the variable. For example:

#!/usr/bin/perl

@days = qw/Mon Tue Wed Thu Fri Sat Sun/;

print "$days[0]\n";

print "$days[1]\n";

print "$days[2]\n";

print "$days[6]\n";

print "$days[-1]\n";

print "$days[-7]\n";

This will produce following result:

Mon

Tue

Wed

Sun

Sun

Mon

Array indices start from zero, so to access first element you need to give 0 as indices. You can also give a negative index, in which case you select the element from the end, rather than the beginning, of the array. This means that

print $days[-1]; # outputs Sun

print $days[-7]; # outputs Mon

Sequential Number Arrays

Perl offers a shortcut for sequential numbers and letters. Rather than typing out each element when counting to 100 for example, we can do something like as follows:

#!/usr/bin/perl

@var_10 = (1..10);

@var_20 = (10..20);

@var_abc = (a..z);

print "@var_10\n";   # Prints number from 1 to 10

print "@var_20\n";   # Prints number from 10 to 20

print "@var_abc\n";  # Prints number from a to z

Here double dot (..) is called range operator. This will produce following result:

1 2 3 4 5 6 7 8 9 10

10 11 12 13 14 15 16 17 18 19 20

a b c d e f g h i j k l m n o p q r s t u v w x y z

Array Size

The size of an array can be determined using scalar context on the array - the returned value will be the number of elements in the array:

@array = (1,2,3);

print "Size: ",scalar @array,"\n"

The value returned will always be the physical size of the array, not the number of valid elements. You can demonstrate this, and the difference between scalar @array and $#array, using this fragment as follows:

#!/uer/bin/perl

@array = (1,2,3);

$array[50] = 4;

$size = @array;

$max_index = $#array;

print "Size:  $size\n";

print "Max Index: $max_index\n";

This will produce following result:

Size: 51

Max Index: 50

There are only four elements in the array that contain information, but the array is 51 elements long, with a highest index of 50.

Adding and Removing Elements in Array

Perl provides a number of useful functions to add and remove elements in an array. You may have a question what is a function? So far you have used print function to print various values. Similarly there are various other functions or sometime called sub-routines which can be used for various other functionalities.

S.N.	Types and Description
1	push @ARRAY, LIST Pushes the values of the list onto the end of the array.
2	pop @ARRAY Pops off and returns the last value of the array.
3	shift @ARRAY Shifts the first value of the array off and returns it, shortening the array by 1 and moving everything down.
4	unshift @ARRAY, LIST Prepends list to the front of the array, and returns the number of elements in the new array.

#!/usr/bin/perl

# create a simple array

@coins = ("Quarter","Dime","Nickel");

print "1. \@coins  = @coins\n";

# add one element at the end of the array

push(@coins, "Penny");

print "2. \@coins  = @coins\n";

# add one element at the beginning of the array

unshift(@coins, "Dollar");

print "3. \@coins  = @coins\n";

# remove one element from the last of the array.

pop(@coins);

print "4. \@coins  = @coins\n";

# remove one element from the beginning of the array.

shift(@coins);

print "5. \@coins  = @coins\n";

This will produce following result:

1. @coins = Quarter Dime Nickel

2. @coins = Quarter Dime Nickel Penny

3. @coins = Dollar Quarter Dime Nickel Penny

4. @coins = Dollar Quarter Dime Nickel

5. @coins = Quarter Dime Nickel

Slicing Array Elements

You can also extract a "slice" from an array - that is, you can select more than one item from an array in order to produce another array.

#!/usr/bin/perl

@days = qw/Mon Tue Wed Thu Fri Sat Sun/;

@weekdays = @days[3,4,5];

print "@weekdays\n";

This will produce following result:

Thu Fri Sat

The specification for a slice must a list of valid indices, either positive or negative, each separated by a comma. For speed, you can also use the .. range operator:

#!/usr/bin/perl

@days = qw/Mon Tue Wed Thu Fri Sat Sun/;

@weekdays = @days[3..5];

print "@weekdays\n";

This will produce following result:

Thu Fri Sat

Replacing Array Elements

Now we are going to introduce one more function called splice(), which has following syntax:

splice @ARRAY, OFFSET [ , LENGTH [ , LIST ] ]

This function will remove the elements of @ARRAY designated by OFFSET and LENGTH, and replaces them with LIST, if specified. Finally it returns the elements removed from the array. Following is the example:

#!/usr/bin/perl

@nums = (1..20);

print "Before - @nums\n";

splice(@nums, 5, 5, 21..25);

print "After - @nums\n";

This will produce following result:

Before - 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

After - 1 2 3 4 5 21 22 23 24 25 11 12 13 14 15 16 17 18 19 20

Here actual replacement begins with the 6th number after that five elements are then replaced from 6 to 10 with the numbers 21, 22, 23, 24 and 25.

Transform Strings to Arrays

Let's look into one more function called split(), which has the following syntax:

split [ PATTERN [ , EXPR [ , LIMIT ] ] ]

This function splits a string into an array of strings, and returns it. If LIMIT is specified, splits into at most that number of fields. If PATTERN is omitted, splits on whitespace. Following is the example:

#!/usr/bin/perl

# define Strings

$var_string = "Rain-Drops-On-Roses-And-Whiskers-On-Kittens";

$var_names = "Larry,David,Roger,Ken,Michael,Tom";

# transform above strings into arrays.

@string = split('-', $var_string);

@names  = split(',', $var_names);

print "$string[3]\n";  # This will print Roses

print "$names[4]\n";   # This will print Michael

This will produce following result:

Roses

Michael

Transform Arrays to Strings

We can use the join() function to rejoin the array elements and form one long scalar string. This function has following syntax:

join EXPR, LIST

This function joins the separate strings of LIST into a single string with fields separated by the value of EXPR, and returns the string. Following is the example:

#!/usr/bin/perl

# define Strings

$var_string = "Rain-Drops-On-Roses-And-Whiskers-On-Kittens";

$var_names = "Larry,David,Roger,Ken,Michael,Tom";

# transform above strings into arrays.

@string = split('-', $var_string);

@names  = split(',', $var_names);

$string1 = join( '-', @string );

$string2 = join( ',', @names );

print "$string1\n";

print "$string2\n";

This will produce following result:

Rain-Drops-On-Roses-And-Whiskers-On-Kittens

Larry,David,Roger,Ken,Michael,Tom

Sorting Arrays

The sort() function sorts each element of an array according to ASCII Numeric standards. This function has following syntax:

sort [ SUBROUTINE ] LIST

This function sorts the LIST and returns the sorted array value. If SUBROUTINE is specified then specified logic inside the SUBTROUTINE is applied while sorting the elements.

#!/usr/bin/perl

# define an array

@foods = qw(pizza steak chicken burgers);

print "Before: @foods\n";

# sort this array

@foods = sort(@foods);

print "After: @foods\n";

This will produce following result:

Before: pizza steak chicken burgers

After: burgers chicken pizza steak

Please note that sorting is performed based on ASCII Numeric value of the words. So the best option is to first transform every element of the array into lowercase letters and then perform the sort function.

The $[ Special Variable

So far you have seen simple variable we defined in our programs and used them to store and print scalar and array values. Perl provides numerous special variables which have their predefined meaning.

We have a speciall variable which is written as $[. This special variable is a scalar containing the first index of all arrays. Because Perl arrays have zero-based indexing, $[ will almost always be 0. But if you set $[ to 1 then all your arrays will use on-based indexing. It is recommended not to use any other indexing other than zero. However, let's take one example to show the usage of $[ variable:

#!/usr/bin/perl

# define an array

@foods = qw(pizza steak chicken burgers);

print "Foods: @foods\n";

# Let's reset first index of all the arrays.

$[ = 1;

print "Food at \@foods[1]: $foods[1]\n";

print "Food at \@foods[2]: $foods[2]\n";

This will produce following result:

Foods: pizza steak chicken burgers

Food at @foods[1]: pizza

Food at @foods[2]: steak

Merging Arrays

Because an array is just a comma-separated sequence of values, you can combine them together as shown below:

#!/usr/bin/perl

@numbers = (1,3,(4,5,6));

print "numbers = @numbers\n";

This will produce following result:

numbers = 1 3 4 5 6

The embedded arrays just become part of the main array as shown below:

#!/usr/bin/perl

@odd = (1,3,5);

@even = (2, 4, 6);

@numbers = (@odd, @even);

print "numbers = @numbers\n";

This will produce following result:

numbers = 1 3 5 2 4 6

Selecting Elements from Lists

The list notation is identical to that for arrays - you can extract an element from an array by appending square brackets to the list and giving one or more indices:

#!/usr/bin/perl

$var = (5,4,3,2,1)[4];

print "value of var = $var\n"

This will produce following result:

value of var = 1

Similarly, we can extract slices, although without the requirement for a leading @ character:

#!/usr/bin/perl

@list = (5,4,3,2,1)[1..3];