How to conditionally include one of two files in a .war package with Buildr?

Question

We're using Buildr to package an application as a .war file. To streamline the automated deployment process further, I'd like to conditionally select one of these two files (from the directory src/main/resources)...

• database-hsql.properties
• database-postgres.properties

...and have it included in the resulting .war with the name database.properties. (In the same place inside the WAR, namely WEB-INF/classes/, where files from src/main/resources now end up.)

Any simple way to do this? Any approach would be fine — e.g. parameterising "package" (somehow) or defining two different tasks/targets (I'm not sure of the terminology) such as "package-hsql" & "package-pgsql" — as long as it works and is simple enough.

Relevant bits of buildfile:

load 'dependencies' 
require 'buildr/hibernate'

desc "..."
define "foo" do

  project.version = VERSION_NUMBER
  project.group = GROUP
  manifest["Implementation-Vendor"] = COPYRIGHT
  compile.with WICKET,GUAVA,GSON, ... [many more libs]
  test.with MOCKITO
  resources

  test.compile.with SERVLET,_('src/main/webapp'),_('src/main/resources')
  package(:war).with(:libs=> [WICKET,GUAVA,GSON, ... ])

end

Bonus question: how to execute an arbitrary shell command (I'd use something involving e.g. >> or sed) in each of the two cases to make changes to another config file? (I'd also want to "inject" some db settings to applicationContext.xml from another file; this would be preferable to keeping two copies of that file in VCS with mostly identical content.)

Sorry if this is too basic; I'm a total newbie with Buildr, and don't really know Ruby. (And yes, it's not an optimal situation to be using a tool that no current team member is proficient with...) If anything needs clarifying, please point it out!

Answer 1

The usual way to parameterize a buildr build is with environment variables. So for instance you might design your build to be executed like so:

$ buildr package DATABASE=postgres

In your buildfile you might then have:

ENV['DATABASE'] ||= 'hsql' # this line makes the default 'hsql'

define "foo" do
  # the rest of the definition

  resources.enhance do
    cp _(:source, :main, :resources, "database-#{ENV['DATABASE']}.properties"), _(:target, :resources, "database.properties")
  end
end

This is the simplest solution; one thing you might consider a drawback is that it will copy the two database-*.properties files in addition to the database.properties file that you'll actually use. If that's a problem it could be worked around at the cost of some more complexity.

Bonus answer: You can execute an arbitrary shell command using system. E.g., at the cost of subshelling I could have implemented the above as:

resources.enhance do
  system("cp '#{_(:source, :main, :resources, "database-#{ENV['DATABASE']}.properties")}' '#{_(:target, :resources, "database.properties")}'")
end

If you are wanting to inject properties into a configuration file, you might want to look at Buildr's filter mechanism.