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Latest revision as of 17:45, 5 October 2017
| Time | Narration |
| 00:01 | Welcome to the Spoken Tutorial on how to use Perl Module Library i.e. CPAN |
| 00:08 | In this tutorial, we will learn to use existing modules and create new modules in PERL. |
| 00:16 | To record this tutorial, I am using:
Ubuntu Linux 12.04 operating system Perl 5.14.2 and 'gedit' Text Editor. |
| 00:28 | You can use any text editor of your choice. |
| 00:32 | To follow this tutorial, you should have working knowledge of Perl programming. |
| 00:37 | If not, then go through the relevant Perl spoken tutorials on the spoken tutorial website. |
| 00:43 | Modules:
These are code files that contain common routines That are written by different authors And, can be used by several programs at a time. |
| 00:55 | CPAN:PERL is an open source language and anyone can contribute to PERL's standard CPAN library. |
| 01:03 | CPAN has thousands of ready-to-use modules written by different authors. |
| 01:09 | The official website of CPAN is:
www.cpan.org |
| 01:17 | We will take List colon colon Util as an example and see how to use it. |
| 01:24 | This gives me access to the functions which are already written inside this module. |
| 01:30 | Switch to the terminal. |
| 01:32 | Type: perldoc List colon colon Util. |
| 01:38 | You may get an error saying You need to install the perl hyphen doc package to use this program. |
| 01:46 | This indicates, you need to install the perl hyphen doc package. |
| 01:50 | Do so using Synaptic Package Manager. |
| 01:55 | Please refer to the relevant Linux spoken tutorials on the spoken tutorial website. |
| 02:01 | What you see here is the documentation for the List colon colon Util module. |
| 02:08 | Note that the documentation contains-
description of the module, example of how to use it and an overview. |
| 02:20 | Hit the 'Q' key to exit the perldoc viewer. |
| 02:25 | Next, we will see how to use List colon colon Util module in a Perl program. |
| 02:33 | Let me open a sample program exist underscore modules.pl which I have already saved. |
| 02:40 | In your exist underscore modules dot pl file, type the following code as displayed on the screen. |
| 02:47 | Let us understand the code now. |
| 02:50 | use List colon colon Util tells Perl to find and load the module List colon colon Util. |
| 03:00 | qw() function extracts words out of the string using a delimiter and returns the words as a list. |
| 03:09 | It is just a quick way of declaring an array. |
| 03:13 | While importing a module, it imports only the subroutines specified in the list into our program. |
| 03:21 | It contains general-utility list of subroutines. |
| 03:26 | The module will export its subroutines and variables into our program. |
| 03:32 | The most popular subroutines available in List colon colon Util are:
first - which returns the first element in the list. |
| 03:42 | max –this returns the highest numerical value in the list. |
| 03:47 | maxstr- returns the highest string in the list. |
| 03:52 | min- this returns the lowest numerical value. |
| 03:57 | minstr – returns the lowest string in the list. |
| 04:02 | shuffle – this returns the values of the input in a random order. |
| 04:08 | sum – returns the numerical sum of all the elements in the list. |
| 04:14 | There is no need to write separate source code for each function. |
| 04:18 | We can just make use of these available subroutines in our program. |
| 04:23 | These are the inputs I am passing to the function max, min, sum and shuffle. |
| 04:30 | And, these are the print statements. |
| 04:33 | Now, press Ctrl+S to save the file. |
| 04:37 | Let us execute the program. |
| 04:40 | Switch back to the terminal and type: perl exist underscore modules dot pl and press Enter. |
| 04:49 | Observe the output. |
| 04:51 | In Random number, you may get any value between 0 and 51. |
| 04:58 | Next, we will see how to create a new Perl module and add it to CPAN. |
| 05:04 | Below are the steps to create a module: |
| 05:08 | Create a place to develop the module. |
| 05:11 | Create skeleton files for the module. |
| 05:14 | Document the module. |
| 05:16 | Write the Perl code. |
| 05:18 | Write the code for testing. |
| 05:20 | Distribute the module in CPAN. |
| 05:24 | Perl is distributed with a program called h2xs which is used to generate files for a new module. |
| 05:32 | Math colon colon Simple specifies our module name. |
| 05:37 | This is used to generate the directory which should clearly identify the module it contains. |
| 05:43 | Basically, it creates skeleton files for the module. hyphen PAX are options that omit autoload and autogenerate. |
| 05:54 | Let's create a new module- Math colon colon Simple. |
| 05:59 | It will be provided with simple functions: add, subtract, multiply and divide. |
| 06:06 | Let us switch to terminal to execute the h2xs command. |
| 06:12 | Type: h2xs hyphen PAXn Math colon colon Simple. |
| 06:20 | The h2xs program generates all these files required to distribute the module. |
| 06:27 | Let us change directory to Math hyphen Simple. |
| 06:33 | Note the directory path on your machine. It may be as Math forward slash Simple. |
| 06:41 | Type "ls" to list all the files in the directory. We can see the following files. |
| 06:49 | The "Changes" file is where we will keep track of changes, made to our module, when we write new versions. |
| 06:58 | lib subdirectory contains the module. |
| 07:02 | MANIFEST contains a list of files in this directory. |
| 07:07 | Makefile is a Perl program used to create a Unix Makefile. |
| 07:12 | We will use this Makefile to test and install our module. |
| 07:18 | Test scripts will be in 't' subdirectory. |
| 07:22 | The tests are simple Perl scripts, but with a dot t extension used for unit testing. |
| 07:30 | Simple.pm is our module. |
| 07:34 | All these files are generated automatically when we execute the h2xs command. |
| 07:41 | Let us open the simple.pm file. |
| 07:45 | Change the directory to lib forward slash Math. |
| 07:51 | Now, we will open the simple.pm file to see the existing content. |
| 07:57 | Type: gedit Simple.pm. |
| 08:02 | What we see here is a documented, functional Perl module that doesn't do anything. |
| 08:09 | We have to write the required functions in this file to make it do something. |
| 08:16 | Add the below code after the text: "Preloaded methods go here". |
| 08:22 | Here, we will add four subroutines add, subtract, multiply and divide. |
| 08:29 | Now, press Ctrl+S to save the file. |
| 08:33 | Now, let's create a sample Perl program to test our code that makes sure it is working properly. |
| 08:41 | Let us open the test file Math-Simple.t under the subdirectory 't'. |
| 08:49 | Type: gedit Math-Simple.t |
| 08:55 | Add the following code after the existing code: “Insert your test code below..”. |
| 09:02 | The Print statements will print the output. |
| 09:06 | Now, press Ctrl+S to save the file. |
| 09:10 | Let us run the test script. |
| 09:13 | Type: perl Math-simple.t and press Enter. |
| 09:19 | We see this error message because the Perl script cannot find Simple.pm in its directory. |
| 09:27 | It should look inside the lib directory. How can we rectify this error? |
| 09:33 | Let us see a few options for this. |
| 09:37 | At the rate INC is a special variable that contains a list of directories. |
| 09:43 | Perl modules and libraries can be loaded from these directories. |
| 09:48 | This line of code tells the Perl program to add this directory path to its at the rate INC search directory. |
| 09:57 | Alternately, we can add files to at the rate INC at run time using '-I' option. |
| 10:06 | Now, let us switch to the terminal. |
| 10:10 | I will execute the program using the '-I' command line parameter. |
| 10:16 | So, I will type: perl -Ilib t/Math-Simple.t |
| 10:24 | Here is the output as expected. |
| 10:27 | We have tested the module and it is working fine. |
| 10:31 | Final step is to distribute the module. |
| 10:34 | The general procedure for installing module is to run these commands. |
| 10:40 | Installation involves copying files into the Perl library directory. |
| 10:45 | Most of us don't have permission to copy into this directory. |
| 10:49 | Since Math-Simple isn't a very useful module, I am not demonstrating the installation part. |
| 10:57 | This brings us to the end of this tutorial. Let us summarize. |
| 11:02 | In this tutorial, we learnt to:
Use existing modules Create new modules and how to use in the Perl program. |
| 11:11 | Here is an assignment for you. |
| 11:13 | Use the Text colon colon Wrap module. |
| 11:17 | Make use of the Wrap() function which wraps the input text to form neat paragraphs. |
| 11:24 | Text colon colon Wrap module has a variable- "columns". Set the columns value to 30. |
| 11:31 | Print the text to see the formatted output. |
| 11:35 | The video at the following link summarizes the Spoken Tutorial project.Please download and watch it. |
| 11:42 | The Spoken Tutorial Project team:
conducts workshops using spoken tutorials and gives certificates on passing online tests. |
| 11:51 | For more details, please write to us. |
| 11:55 | Spoken Tutorial project is funded by NMEICT, MHRD, Government of India. |
| 12:02 | More information on this mission is available at this link. |
| 12:06 | This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching. |
