class MyCommand < Rscons::Builder
  def run(target, sources, cache, env, vars)
    vars = vars.merge({
      "_TARGET" => target,
      "_SOURCES" => sources,
    })
    command = env.build_command("${CMD}", vars)
    cmd_desc = vars["CMD_DESC"] || "MyCommand"
    standard_build("#{cmd_desc} #{target}", target, command, sources, env, cache)
  end
end

Rscons::Environment.new do |env|
  env.add_builder(MyCommand.new)
  command = %w[gcc -c -o ${_TARGET} ${_SOURCES}]
  env.MyCommand("simple.o", "simple.c", "CMD" => command)
end