Perl Module Features

Designing and Using a Perl Module – Part 1

Foreword: In this part of the series, I give you features of a Perl Module.

By: Chrysanthus Date Published: 2 Apr 2016

Introduction

This is part 1 of my series, Designing and Using a Perl Module. A Perl module is a file consisting basically of commonly used functions. In this part of the series, I give you features of a Perl Module. I use ActivePerl for the code samples. If you are using traditional Perl, then precede your script with something like, #!/usr/bin/perl .

Pre-Knowledge
At the bottom of this page, you have links to different series you should have read before coming here, to better understand this one.

Meaning of a Module
A module in Perl is a file that has commonly used functions. It can have a few or no variables. The variable types (functions) are coded in a Package. The name of the package is the name of the file. The extension of the filename is .pm . Here, pm, stands for Perl Module. The package name and file name should start with an uppercase letter. The variable types (functions and maybe a few variables) are generally used by many programs written by different developers independently.

Standard Library
Another word for “module” is “library”. The word, library can also mean a set of related modules (i.e. a set of related libraries); at the limit, the modules may have very little relationship between one another. The installation of Perl comes with a very big library. The library is a subdirectory, with sub and sub directories. A related set of modules is found in a subdirectory. If there are many modules in that directory, the more related ones are found in a more sub directory; there is a hierarchy of directories.

In my Windows Operating System the directory for the Perl library is, c:/Perl/lib . The rest of the library subdirectories are in this directory. Many of the modules in this directory can be considered as standard modules, to be used in a standard way by all programmers (developers).

Package
A module is a package. A package is a class. So in a module, you can optionally have instantiated objects and inherited classes. The last expression in a module is just 1 and a semicolon; which means the module returns true (1).

Version
A package should have a version number. Each package has a predefined special version variable to which you can assign the version number. The variable is $VERSION. The version number is a positive number and is typed in quotes, as in "0.01". There should be at least two decimal digits after the decimal point. So you would have a statement like,

$VERSION = "0.01";

in the module. You can use the other version schemes, but I cannot guarantee that they will work with all related software.

Package Types
A package can be created in two ways. You can have a package in blocks or a package in the our scope.

Package as Module
A package (code) as a module is something like:

package pkgName;

our $VERSION = "0.01";

#maybe a few more variables

sub new  #optional
    {
        bless {}, $_[0];
    }

sub aFunc
    {
        //statements
    }

# more functions (sub definitions)

1;

Do not forget to end the module with “1;” .

That is it for this part of the series. We stop here and continue in the next part.

Chrys

Broad Network

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