middleman tutorial

$ cat .ruby-version
2.5.1

$ vi Gemfile
...

$ cat Gemfile
source 'https://rubygems.org'

gem 'middleman', '~> 4.2'

$ rbenv exec bundle install
...

$ rbenv exec bundle exec middleman version
Middleman 4.2.1

$ rbenv exec bundle exec middleman init .
...

$ rbenv exec bundle exec middleman server

$ rbenv exec bundle exec middleman build
      create  build/stylesheets/site.css
      create  build/javascripts/site.js
      create  build/images/.keep
      create  build/index.html
Project built successfully.