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Perl Modules

Perl Modules Maharajan M Vinai AR

Telecom Service Provider Division Wipro Technologies

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Perl Modules

Table of Contents ............................................................................................................................................1 Table of Contents................................................................................................................2 Introduction to PERL Modules..........................................................................................3 What is PERL Module?........................................................................................ ....................3 Why PERL Modules?.............................................................................................................. ..3 Module Structure .............................................................................................. .......................3 Sample PERL Module......................................................................................................... ......6

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Perl Modules

Introduction to PERL Modules What is PERL Module? PERL Module is a file containing related functions designed to be used by programs and other modules. Every module has a set of variables and functions that can be used by the external programs and modules. Why PERL Modules?  Reusable functions can be grouped together and can be imported during compile time.  Required symbols (functions and variables) alone can be imported.  Different levels of public interfaces can be provided using EXPORT, EXPORT_OK and different tags.  By assigning package name to the module, the identifiers/symbols can be associated with a global namespace. Module Structure Structure of any PERL module package <Module name>; use strict; our (@ISA, @EXPORT, @EXPORT_OK, %EXPORT_TAGS, $VERSION); use Exporter; $VERSION = ; @ISA = qw(Exporter); @EXPORT = qw(…); # Symbols to autoexport (:DEFAULT tag) @EXPORT_OK = qw(…);# Symbols to export on request %EXPORT_TAGS = ( TAG1 => […], TAG2 => […], … ); ################### # your code goes here ################### 1;

# This should be the last line.

Package Name:

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Perl Modules

The first line of the code has the package name. Usually the package name and the file name are same. The package name is used to allocate a namespace for the symbols used in the module, so that they won’t interfere with the symbols used in the programs that import this module. E.g.: For a PERL Module Sample, the file name would be Sample.pm and the package name would be Sample. package Sample; The above module can be imported in other PERL programs as below use Sample; If the file Sample.pm is placed under a directory Wipro then the package name should also have the directory name where the file is placed. package Wipro::Sample; To load the above module the use command should be as below use Wipro::Sample; Exporter: The command use Exporter; is used to load the Exporter Module, which manages the modules public interface. Public interface is nothing but the symbols designed for use by other PERL programs and modules. @ISA: The special, per-package array @ISA contains the word “Exporter”. When a user says use Wipro::Sample; perl implicitly calls a special method, Wipro::Sample->import ( ). We don’t have an import method in our package, but that’s okay, because the Exporter package does and we are inheriting from it because of the assignment to @ISA. Perl looks at the package’s @ISA for resolution of undefined methods. $VERSION: When a module is loaded, a minimal required version number can be supplied. If the version isn’t at least high, the use will raise an exception. use <Module name> 2.0 # If $VERSION < 2.0, fail @EXPORT: This array contains the list of functions and variables that will be exported into the caller’s own namespace so they can be accessed without being fully qualified. Typically, a qw( ) list is used.

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Perl Modules

E.g.: @EXPORT = qw(Func1 Func2 @ArrayList); With the simple use <Module name> call, The function Func1 can be called as Func1 ( ) rather than <Module name>::Func1 ( )  The array @ArrayList can be accessed as @ArrayList instead of @<Module name>::ArrayList 

To load a module at compile time but request that no symbols be exported, use the special form use Exporter ( ), with empty parenthesis. @EXPORT_OK: This variable is used to list the symbols that are to be loaded on special requests. E.g: @EXPORT_OK = qw( SpclFunc $SpclVar); The user can load the module like below use <Module name> qw(SpclFunc $SpclVar Func1) and import only the SplcFunc function, the SplcVar scalar variable and the Func1 function. The function Func1 is already listed in the @EXPORT array. The other symbols Func2 function and @ArrayList array listed in @EXPORT array are not imported automatically. The user can also load the module like below use <Module name> qw(:DEFAULT $SpclVar); to import all the symbols listed in @EXPORT array and $SpclVar listed in @EXPORT_OK array. %EXPORT_TAGS: This tag is for creating higher level groupings of related import symbols. The values of these tags are references to arrays of symbol names that are already listed in either @EXPORT or @EXPORT_OK array. E.g.: %EXPORT_TAGS = ( AllFunctions => [ qw(Func1 Func2 SpclFunc) ], AllVariables => [ qw(@ArrayList $SpclVar) ] );

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Perl Modules

An import symbol with a leading colon means to import a whole of symbols. E.g.: use <Module name> qw( :AllFunctions $SpclVar); The above use will import all the functions (Func1, Func2 and SpclFunc) that are listed against the AllFunctions tag and the variable SpclVar. The :DEFAULT tag means all the symbols listed in the @EXPORT array. This module can be called from other PERL files using any of the following commands: use <Module name>; # Import default symbols use <Module name> qw(…); # Import listed symbols use <Module name> ( ); # Do not import any symbols use <Module name> qw(:TAG1); # Import the whole tag set

Sample PERL Module Below is a very simple PERL Module used for integer arithmetic operations like Addition, Subtraction, Multiplication and Division. #!/usr/bin/perl –w package Arithmetic; use strict; our (@ISA, @EXPORT, @EXPORT_OK, %EXPORT_TAGS, $VERSION); use Exporter; $VERSION = 1.0; @ISA = qw(Exporter); @EXPORT = qw(Add Subtract Multiply Divide ); sub Add { my ($val1, $val2) = @_; my ($result); if($val1 !~ /^\d+$/ || $val2 !~ /^\d+$/) { return undef; } $result = $val1 + $val2;

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Perl Modules

return $result; } sub Subtract { my ($val1, $val2) = @_; my ($result); if($val1 !~ /^\d+$/ || $val2 !~ /^\d+$/) { return undef; } $result = $val1 - $val2; return $result; } sub Multiply { my ($val1, $val2) = @_; my ($result); if($val1 !~ /^\d+$/ || $val2 !~ /^\d+$/) { return undef; } $result = $val1 * $val2; return $result; } sub Divide { my ($val1, $val2) = @_; my ($result); if($val1 !~ /^\d+$/ || $val2 !~ /^\d+$/) { return undef; } $result = $val1 / $val2;

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Perl Modules

return $result; } 1;

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