File: README — Documentation for gem2rpm (0.10.1)

This package is a first attempt at converting ruby gems to rpm’s. Because of the differences between the two packaging schemes, it is impossible to come up with a completely automated way of doing the conversion, but the spec files produced by this package should be good enough for most pure-ruby gems. I wouldn’t put too much hope into automating the gem->rpm process for gems with binary code such as database drivers. But even for those, gem2rpm provides a good starting point for the packaging gems as RPM’s.

Installation

Download the ruby gem or an RPM (TODO: more detail)

Usage

Run ‘gem2rpm –help’ for options

At its simplest, download a gem (let’s call it GEM) in its latest version (e.g. 1.2.3):

$ gem fetch GEM

and run gem2rpm above the downloaded file:

$ gem2rpm GEM-1.2.3.gem

You can also use the –fetch flag to fetch the (latest) gem before generating the spec file, achieving the same effect as running ‘gem fetch GEM’ plus ‘gem2rpm GEM-1.2.3.gem’:

$ gem2rpm --fetch GEM

This will print an rpm spec file based on the information contained in the gem’s spec file. In general, it is necessary to edit the generated spec file because the gem is missing some important information that is customarily provided in rpm’s, most notably the license and the changelog.

Rather than editing the generated specfile, edit the template from which the specfile is generated. This will make it easier to update the RPM when a new version of the Gem becomes available.

To support this process, it is recommended to first save the default template somewhere:

gem2rpm -T > rubygem-GEM.spec.template

Now, edit the template and then run gem2rpm to generate the spec file using the edited template:

gem2rpm -t rubygem-GEM.spec.template > rubygem-GEM.spec

With that, you can now build your RPM as usual. When a new version of the gem becomes available, you should edit the saved template and rerun gem2rpm over it.

Template Details

The template is a standard erb file; there are two main variables available in the template file:

package      - The Gem::Package for the gem
spec         - The Gem::Specification for the gem (the same as format.spec)

Deprecated:

format       - The Gem::Format for the gem. Please note that this is kept
               just for compatibility reasons, since RubyGems 2.0 removed
               this class.

Conventions

A typical source RPM for a gem should consist of three files: the gem file itself, the template for the spec file and the spec file. To ensure that the template will be included in the source RPM, it must be listed as one of the sources in the spec file.

The resulting rpms should follow the naming convention ‘rubygem-$GEM’ where GEM is the name of the packaged gem. The default template also makes sure that the resulting package provides ‘ruby($GEM)’, according to general packaging conventions for scripting languages.

Gem Limitiations

Gem has some important limitations that make it next to impossible to fully automate the gem -> rpm conversion process. Amongst them are

- No license field
- No changelog
- No distinction between build and install time (important for gems with
  binary components)
- Because of its nature as a separate packaging system, gems can not
  capture dependencies on non-gem system components, e.g., the ruby
  PostgreSQL driver can not properly describe its build- and
  runtime-dependencies on the various pieces of the PostgreSQL database