I've written several Rake tasks in the past that could have been improved by accepting parameters, but I never knew how to make it work. It's not that I thought it was impossible to pass parameters to Rake tasks, I just never bothered to figure out how. Lucky for me, a teammate recently took the time to figure it out. Today I'm changing an existing rakefile to take advantage of passing in parameters.

The file now:

require 'writer'
require 'html_writer'
require 'doc_writer'

directory "built_docs"
directory "built_html"

task :doc => [:built_docs, :clean_doc] do
  Dir['chapters/*.txt'].each do |chapter|
    output = "built_docs/#{File.basename(chapter,'txt')}doc"
    File.open(output, 'w') { |file| DocWriter.new(file).write(chapter) }
    puts "generated #{output}"
    system "chmod 444 #{output}"
  end
end

task :html => [:built_html, :clean_html] do
  Dir['chapters/*.txt'].each do |chapter|
    output = "built_html/#{File.basename(chapter,'txt')}html"
    File.open(output, 'w') { |file| HtmlWriter.new(file).write(chapter) }
    puts "generated #{output}"
    system "chmod 444 #{output}"
  end
end

task :clean_doc do
  Dir['built_docs/*'].each do |output|
    rm output
  end
end

task :clean_html do
  Dir['built_html/*'].each do |output|
    rm output
  end
end

Clearly, this file is not near as DRY as it could be.

The first step is to create a new task that will generate output and accept the format as an argument.

task :default do
  unless ENV.include?("output") && (ENV['output']=='doc' || ENV['output']=='html')
    raise "usage: rake output= # valid formats are [html] or [doc]" 
  end
  format = ENV['output']
  puts format
  rm_rf format
  mkdir format
end

The above code verifies that a valid format is specified. It also removes the need for both the directory and clean tasks. The only work left to do is combine the output generation tasks.

task :default do
  unless ENV.include?("output") && (ENV['output']=='doc' || ENV['output']=='html')
    raise "usage: rake output= # valid formats are [html] or [doc]" 
  end
  format = ENV['output']
  puts format
  rm_rf format
  mkdir format
  Dir['chapters/*.txt'].each do |chapter|
    output = "#{format}/#{File.basename(chapter,'txt')}#{format}"
    writer = (format=='doc' ? DocWriter : HtmlWriter)
    File.open(output, 'w') { |file| writer.new(file).write(chapter) }
    puts "generated #{output}"
    system "chmod 444 #{output}"
  end
end

The resulting task is cleaner and easier to maintain.