After that, we need to configure our MRuby build. We need to modify build_config.rb. At the end of the file, let’s add our build specification. MRuby::Build.new('mrubyvst') do |conf| toolchain :gcc conf.gembox 'default' conf.gem :core => 'mruby-eval' conf.gem :github => 'iij/mruby-dir' conf.gem :github => 'iij/mruby-io' end In this case, we specify that we will use a gcc toolchain. Also, we will i