Using Array Variables

Perl Tutorials - Herong's Tutorial Examples

∟Using Array Variables

This section describes how an array variable can be assigned with a list value. Array elements are referred by subscription notation as scalar expressions, like $identifier[i]. An unassigned array variable contains the (undef) value.

Array variables can be used in a Perl script under these rules:

An array variable should be assigned with a list value constructor using an assignment operation. For example, @links = ("herongyang.com", "perl.org", "cpan.org").
Each element in an array variable can be referenced by a scalar expression with the index subscription notation, $identifier[i]. The index i represents the ordered position of this element. The index value of the first element is 0. For example, $links[0] is a scalar expression refers to the first element of the array variable @links.
Negative indexes can be used in the index subscription notation to refer array elements counted backward. For example, $links[-1] is a scalar expression referring to the last element of the array variable @links.
The last index value of an array variable can be obtained by a special scalar value, $#identifier. For example, $#links is a scalar value represents to the last index of the array variable @links. One way to calculate the number of elements in an array is to use this last index notation, like $#links + 1.
If a new value is assigned to an element index value beyond the current last index, the array will be extended to the new index value.
If you are trying to access an element with an index that has no value assigned, you will get the undef value. For example, $links[$#links+1] is an undefined value, undef, because no value is assigned to an index beyond the current last index.

Here are some examples of array variable assignment operations with list value constructors:

   @messages = 'hello';
   @primes = 3,5,7,11;
   @vacations = 'Mon','Tue','Wed';
   @vacations = ('Mon','Tue','Wed');
   @vacations = (Mon,Tue,Wed);
   @menu = 'Mon',2,'Apple';
   @dates = 'Jan',31,'Feb',28,'Mar',31;

Here is a Perl tutorial script on how to use array variables:

#- ArrayVariable.pl
#- Copyright (c) HerongYang.com. All Rights Reserved.
#
   @links;                             # Undefined
   print(@links, "\n");

   @links = ("herongyang.com", "perl.org", "cpan.org");
   print(@links, "\n");                # Defined now

   $url = $links[0];                   # Refers to the first element
   print($url, "\n");

   $links[2] = "google.com";           # Updates the 3rd element
   print($links[2], "\n");

   $links[9] = "yahoo.com";            # Extending the array size
   print($links[9], "\n");

   print($links[-10], "\n");           # Backward index

   $size = $#links + 1;                # last index value
   print($size, "\n");

   print ("undef", "\n") if ($links[100] == undef);
                                       # Out of bound index

Here is the output of the tutorial script:


herongyang.comperl.orgcpan.org
herongyang.com
google.com
yahoo.com
herongyang.com
10
undef

Table of Contents

About This Book

Perl on Linux Systems

Perl on macOS Computers

ActivePerl on Windows Systems

►Data Types: Values and Variables

Scalar Values and List Values

Scalar Value Constructors

Scalar Value Interpretation

List Value Constructors

Variables - Scalar, Array and Hash

Using Scalar Variables

►Using Array Variables

Using Hash Variables

"undef" Value and Undefined Variables

Expressions, Operations and Simple Statements

User Defined Subroutines

Perl Built-in Debugger

Name Spaces and Perl Module Files

Symbolic (or Soft) References

Hard References - Addresses of Memory Objects

Objects (or References) and Classes (or Packages)

Typeglob and Importing Identifiers from Other Packages

String Built-in Functions and Performance

File Handles and Data Input/Output

Open Files in Binary Mode

Open Directories and Read File Names

File System Functions and Operations

Image and Picture Processing

Using DBM Database Files

Using MySQL Database Server

Socket Communication Over the Internet

XML::Simple Module - XML Parser and Generator

XML Communication Model

SOAP::Lite - SOAP Server-Client Communication Module

Perl Programs as IIS Server CGI Scripts

CGI (Common Gateway Interface)

XML-RPC - Remote Procedure Call with XML and HTTP

RPC::XML - Perl Implementation of XML-RPC

Integrating Perl with Apache Web Server

CGI.pm Module for Building Web Pages

LWP::UserAgent and Web Site Testing

Converting Perl Script to Executable Binary

CPAN (Comprehensive Perl Archive Network)

Archived Tutorials

References

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