SubParamAlias.pl - Example on Parameters as Alias

This section provides a tutorial example on how parameters are passed as aliases - modifying the value of a parameter will cause the value of the original variable updated in caller's code.

As mentioned in the previous section, all parameters are passed as aliases. If the value of a parameter is modified inside a subroutine, the value of the corresponding variable in the calling code is also modified. But if the calling code is passing a literal as a parameter, then you can not modify the value of this parameter. You will get an execution error.

Here is a tutorial example on parameters passed as aliases into a subroutine:

#- SubParamAlias.pl
#- Copyright (c) 1995 by Dr. Herong Yang, http://www.herongyang.com/
#
   $a = 'hello';
   @a = ('mon','tue','wed','thu','fri');
#   &subParamAlias('world');
   &subParamAlias($a);
   print $a, "\n";
   &subParamAlias(@a);
   print join(',',@a), "\n";
   exit;
sub subParamAlias {
   foreach (@_) {
      tr/a-z/A-Z/;
   }
}

Here is the output of the tutorial script:

HELLO
MON,TUE,WED,THU,FRI

The output clearly shows you that modifying the parameter array directly will cause value changes on the caller's variables.

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

 Declaring and Calling Subroutines

 SubParamList.pl - Example on Parameter List

SubParamAlias.pl - Example on Parameters as Alias

 SubReturnValue.pl - Example on Return Values

 SubCalling.pl - Example on Calling Formats

 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

 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