CPAN PLUS

by Jos Boumans
March 26, 2002

Setting: A warm August day, somewhere in Amsterdam. In the bar of Yet Another Hotel. A large number of people are gathered. Judging by their attire, they're not here for business -- or at least not the business of selling vacuum cleaners. They notice the sun and appreciate it, but it is the shining light of their laptops that captivates them.

A man with long dark hair stands up -- he appears to be the leader of this unusal congregation. He's wearing overalls and is barefoot.

He begins to speak of something called "see pants," which has the potential to change the world of the laptop-people. It would alter the way free software is distributed. It would receive a mark of quality; it would be tested and reviewed. And gosh darnit, it would be good.

Related Reading Programming Perl, 3rd Edition By Larry Wall, Tom Christiansen, Jon Orwant Table of Contents Index Sample Chapter Read Online--Safari

That man was Michael Schwern. His idea was CPANTS, the "CPAN Testing Service," and the occasion was YAPC::Europe 2001. But CPANTS required work. Each of us set off with our own little part, trying to make the world a better place.

Being a novice to the Perl community and eager for a challenging project to sink my teeth into, I offered to patch CPAN.pm so that CPANTS could automatically build modules and test them. I imagined this would be a simple role.

I started looking through the sources of CPAN.pm. Although in my experience as a user, CPAN.pm had always worked as advertised, as a developer I was confronted with its limitations: It was not very modular, allowing few additions to its functionality; it had a limited programming interface, being basically designed for interactive use.

So there I stood, having made a commitment to ameliorate the CPAN-interface and lacking the code base to do so, with two choices: Complain or Fix. Since complaining wouldn't give the desired result, the only remaining option was to start anew.

Thus CPANPLUS was born. Its objective is simple: do what CPAN.pm does, but do it better. We'd start with a clean code base designed to accommodate different types of use. But at the same time, this code should be a starting point, not the end point.

So is CPANPLUS better? That's for you to decide. The project began in October 2001, and late March 2002 marks the first official release on CPAN, timed to accompany this article.

Setting Up CPANPLUS

Setting up CPANPLUS should be simple. It is installed like any other Perl module:

    perl Makefile.PL
    make
    make test
    make install

The setup of CPANPLUS happens with "perl Makefile.PL." CPANPLUS will attempt to do two things at this point:

• write an appropriate configuration for your system; and
• probe for modules CPANPLUS would like to have, but which are not required.

Currently, the configuration is not automatic, so you will be prompted to answer some questions about your system, although in many cases the default values are acceptable. CPANPLUS will then fetch the index files for the first time and ask you to choose your favorite CPAN mirrors. You can pick from a list, or specify your own.

One question remains: Should we probe for missing modules? It is recommended that you do so, because CPANPLUS is faster and better with those modules installed. It's up to you, however: CPANPLUS does not require any noncore modules to run.

Continue with make and make test. All tests should pass -- if they don't, something is wrong. A list of tested platforms is available at the CPANPLUS FAQ site. Finally, run "make install" and CPANPLUS will be installed on your system!

The Structure of CPANPLUS

As you may have noticed if you've looked at the sources, CPANPLUS is spread out over many modules. This is because of heavy subclassing: We believe that each specific task should have its own space in the CPANPLUS library. This modular build allows for extensions to the library and many plugins.

There are two modules that are of particular interest to users of CPANPLUS. One is the user-interface CPANPLUS::Shell, and the other is the programming-interface CPANPLUS::Backend. Both modules will be explained in more depth later. Two other modules allow you to alter the behavior of the library at run time. These are CPANPLUS::Error, which allows you to manipulate error messages to and from CPANPLUS; and CPANPLUS::Configure, which allows you to change the configuration at runtime. They're definately worth looking at if you are a developer using CPANPLUS.

The User's Interface: 'Shell'

In truth, it isn't fair to say that "Shell" is the user's interface; CPANPLUS is designed to work with any number of shells. In fact, if you want to write your own shell, then that's possible. At the moment, only the default shell exists, but Jouke Visser is at work on a wxPerl shell.

You can specify which shell you wish to run in your configuration file. The default is CPANPLUS::Shell::Default.

There are two ways to invoke the shell. One is the familiar way:

perl -MCPANPLUS -eshell

There is also an executable in your Perl bin directory:

cpanp

The -M syntax also accepts a few flags that allow you to install modules from the command line. See the perldoc for CPANPLUS for details.

Now let's look at using the default shell.

One of its features is that each command works with a single letter. This could be called the "compact shell" as it is designed to be small, but still provide all the basic commands you need.

Here is a short summary of the command options available, which can also be seen by typing "h" or "?" at the shell prompt:

    a AUTHOR [ AUTHOR]    Search by author or authors
    m MODULE [ MODULE]    Search by module or modules
    i MODULE | NUMBER     Install a module by name or previous result
    d MODULE | NUMBER     Download a module to the current directory
    l MODULE [ MODULE]    Display detailed information about a module
    e DIR    [ DIR]       Add directories to your @INC
    f AUTHOR [ AUTHOR]    List all distributions by an author
    s OPTION VALUE        Set configuration options for this session
    p [ FILE]             Print the error stack (optionally to a file)
    h | ?                 Display help
    q                     Exit the shell

Let's assume you want to see whether you can install a module in the Acme:: namespace.

First, you'd look for modules that match your criteria with a module search:

m ^acme::

As you can see, a search can take a regular expression. It's a feature of the default shell that all searches are case-insensitive.

This search will return a result like this:

    0001  Acme::Bleach          1.12    DCONWAY
    0002  Acme::Buffy           undef   LBROCARD
    0003  Acme::Colour          0.16    LBROCARD
    0004  Acme::ComeFrom        0.05    AUTRIJUS
    0005  Acme::DWIM            1.05    DCONWAY

The first number is simply the ID for this search, which can be used as a shortcut for subsequent commands. The next column is the name of the module, followed by a version number. The last is the CPAN id of the author.

Imagine you'd like to get more information about Acme::Buffy. Simply type:

 l Acme::Buffy

Or, to save effort, the ID from the most recent search can be used:

l 2

This will give results like this:

  Details for Acme::Buffy:
  Description               An encoding scheme for Buffy fans
  Development Stage         Released
  Interface Style           hybrid, object and function interfaces available
  Language Used             Perl-only, no compiler needed, should be platform independent
  Package                 Acme-Buffy-1.2.tar.gz
  Support Level             Developer
  Version                   undef

If "Acme::Buffy" looks appealing, then you can install it:

i 2

That's all you need to install modules with CPANPLUS.

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