Perl Tutorials - Herong's Tutorial Examples - Version 5.32, by Dr. Herong Yang

Perl Tutorials - Herong's Tutorial Examples

∟Hard References - Addresses of Memory Objects

∟\* - Creating Hard References

Hard references are pointers (or addresses) of other variables, functions, or any objects. Hard references are stored in scalar variables. They can be created in several ways.

1. Using the backslash operator, \, on a variable or a function to create a hard reference for that variable or function, as in the following examples:

   $r1 = \$a;
   $r2 = \@b;
   $r3 = \%c;
   $r4 = \&d;

There are three special usages of the backslash operator, \:

1.1. Using the backslash operator, \, on an expression that returns a scalar to create a hard reference to an anonymous scalar (not assigned to any variable name), as in the following examples:

   $r1 = \1;
   $r2 = \'foo';
   $r3 = \(1+1);

1.2. Using the backslash operator, \, on an list object enclosed in parentheses to create a list of hard references to all elements in the list object, as in the following examples:

   @r1 = \(Mon, Tue, Wed); # same as (\'Mon',\'Tue',\'Wed')
   @r2 = \(@b); # not the same as \@b

1.3. Using the backslash operator, \, on a hard reference to create a hard reference of the specified hard reference, as in the following examples:

   $r1 = \$a;
   $r2 = \$r1;
   $r3 = \\\%c;

2. Using square brackets on a list object to create a hard reference for an anonymous array (not assigned to any variable name), as in the following examples:

   $r1 = [3,5,7,11];
   $r2 = [Mon, Tue, Wed];
   $r3 = ['Jan',31,'Feb',28,'Mar',31];

3. Using curly brackets on a list object to create a hard reference for an anonymous hash (not assigned to any variable name), as in the following examples:

   $r1 = {3,5,7,11}; # not very useful
   $r2 = {Mon, Tue, Wed}; # not very useful
   $r3 = {'Jan',31,'Feb',28,'Mar',31};

4. Using "sub" without a name to create a hard reference for an anonymous function (not assigned to any function name), as in the following examples:

   $r1 = sub {print "I am here.\n";}

Table of Contents

 About This Book

 Perl on Linux Systems

 ActivePerl on Windows Systems

 Data Types: Values and 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

►\* - Creating Hard References

 Using Hard References

 $$name - Replacing Identifiers by Scalar Variables

 ${EXPR} - Replacing Identifiers by Expressions

 EXPR->* - The Dereference Operator

 $$$name - Nested Hard References

 \$b-\$a - Using Hard References in Other Operations

 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

 Converting Perl Script to Executable Binary

 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

 References

 PDF Printing Version

\* - Creating Hard References - Updated in 2018, by Dr. Herong Yang