Packaging and Distributing Software

No matter how productive it makes you, a programming language won save you any time if you can take advantage of a body of code written by other people. A community works faster than any one person, and its usually easier to install and learn a library than to write and debug the same code yourself.

That is, if you can find the library in the first place. And if you e not sucked into an mess of dependencies that grow and grow, making you want to write the code yourself just so you can be doing some real programming.

The success of Perls CPAN archive has made the Ruby community work on our own centralized code repository and packaging system. Whatever you think of Perl, you must admit that a Perl programmer can find just about any library they need in CPAN. If you write your own Perl library, you know where to send it: CPAN. This is not really a technical aspect of Perl, but its a powerful component of that languages popularity.

The problem of packaging is more a logistical problem than a technical one. Its a matter of coordination: getting everyone to agree on a single mechanism for installing packages, and a single place to go to find those packages. For Ruby, the installation mechanism is Ruby gems (or rubygems or just "gems"), and rubyforge.org is the place to go to find gems (packaged libraries and programs).

In many recipes in this book, we tell you to use a gem for some task: the alternative is often to show you pages and pages of code. This chapter covers how to find the gems you need, install them, and package your own software as gems so that others can benefit from your work.

You may need to find and install the Ruby gems system itself. It comes installed by default on Windows, but not on Unix. You can download it from this URL:

http://rubyforge.org/frs/?group_id=126

To install the Ruby gems package, unzip the tarball or ZIP file, and run the setup.rb script within. You can then use the gem command to search for and install gems, as described in Recipes 18.1 and 18.2. You can also build your own gems from "gemspec" files, as described in Recipe 18.6, and upload it to RubyForge or some other site (Recipe 18.7).

An older installation system called setup.rb is still in use (for instance, to install the Ruby gems package itself). We cover this mechanism briefly in Recipe 18.8.

Neither Ruby gems nor setup.rb play well with a Unix distributions native package installers. If you use a system like Debian or Red Hat, you may find that some packages (like Rails) are available both as gems and in your native package format. These issues are still being resolved; in the meantime, you should use your native package format whenever possible.