Defining Your Own Perl Module

Perl Tutorials - Herong's Tutorial Examples

Dr. Herong Yang, Version 5.10

Perl Tutorials - Herong's Tutorial Examples

∟Defining Your Own Perl Module

This section provides a tutorial example on how to define your own Perl module with its own name space and stored in a separate script file named as *.pm.

Perl Module - A special source code file that:

Contains variables and subroutines related to a single subject.
Can be used as an include file.
Has its own name space.
Has a file name matches the name space name. File extension should be .pm.

Here is a dummy example of Perl module, MyModule.pm,

#- MyModule.pm
#- Copyright (c) 1995 by Dr. Herong Yang, http://www.herongyang.com/
#
   package MyModule;
   sub BEGIN {
      print("Printing in BEGIN of ",__PACKAGE__,"...\n");
      $begin = "Begin";
   }   	
   sub CHECK {
      print("Printing in CHECK of ",__PACKAGE__,"...\n");
      $check = "Check";
   }   	
   sub INIT {
      print("Printing in INIT of ",__PACKAGE__,"...\n");
      $init = "Init";
   }
   sub END {
      print("Printing in END of ",__PACKAGE__,"...\n");
      $end = "End";
   }
   print("Printing from MyModule.pm...\n");
sub myModuleSub {
   print("Printing from myModuleSub()...\n");
}
1;

And a dummy test script, ModuleTest.pl,

#- ModuleTest.pl
#- Copyright (c) 1995 by Dr. Herong Yang, http://www.herongyang.com/
#
   print("Printing from ModuleTest.pl before MyModule...\n");
   require MyModule;
   print("Printing from ModuleTest.pl after MyModule...\n");
   print("MyModule::begin = $MyModule::begin\n");
   print("MyModule::check = $MyModule::check\n");
   print("MyModule::init = $MyModule::init\n");
   print("MyModule::end = $MyModule::end\n");
   &MyModule::myModuleSub();
   exit;

Here is the output of the test script:

Printing from ModuleTest.pl before MyModule...
Printing in BEGIN of MyModule...
Printing from MyModule.pm...
Printing from ModuleTest.pl after MyModule...
MyModule::begin = Begin
MyModule::check =
MyModule::init =
MyModule::end =
Printing from myModuleSub()...
Printing in END of MyModule...

A couple of notes here:

If you use bare word in the require function, it will automatically append .pm, and use it as the module file name.
The output shows that CHECK() and INIT() were not executed. I don't know why.
The output shows that BEGIN() in MyModule.pm was executed during the compilation process of MyModule.pm, but that was in the middle of the execution of the calling program, ModuleTest.pl.
The output also shows that END() in MyModule.pm was not executed at the end of the execution process of MyModule.pm. It was executed at the end of the entire execution - end of ModuleTest.pl.

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

Including Script Codes from Other Files

do() Function - Including Script Files

require() Function - Including Script Files