make-rake-completion-for-fish.rb

out = `rake --help`

sss = out.lines.map(&:strip).grep(/^-/).map {|s|
  opt = /(?:-¥w|--[-¥w]+?)/
  arg = /¥[?([A-Z]+)¥]?/

  s.match(/(#{opt}(?:, #{opt})*)(?: #{arg})? {2,}(.*)/).to_a[1..-1]
}.reject(&:nil?)

hs = sss.map {|opts, arg, desc|
  opts.split(/, /).inject(:short => [], :long => []) {|h, opt|
    case opt
    when /^--([-¥w]+)$/
      h.tap {|i| i[:long] << $1 }
    when /^-(¥w)$/
      h.tap {|i| i[:short] << $1 }
    else
      raise opt
    end
  }.merge(:arg => arg, :desc => desc)
}

puts hs.map {|h|
  short = h[:short].map {|s| "-s #{s}" }
  long = h[:long].map {|s| "-l #{s}" }
  desc = (d = h[:desc]) ? "-d #{d.inspect}" : ''

  ['complete -c rake', short, long, desc].reject(&:empty?).join(' ')
}.join("¥n")