Read and specify ruby version in Gemfile from asdf-vm .tool-versions file.

ruby_version.rb

# https://gist.github.com/EdwardDiehl/9c660b59d0fb2e936774ee2c4fcfc792
# Read and specify ruby version in Gemfile from asdf-vm .tool-versions file.
# Copy the file to your your project root.
# Add these lines at the top of your project Gemfile:
# require './ruby_version.rb'
# ruby ruby_version

def ruby_version(ruby_default_version = '2.5.0')
  tool_versions_file = File.join(File.expand_path('..', __FILE__), '.tool-versions')

  if File.readable?(tool_versions_file)
    ruby_version = IO.foreach(tool_versions_file, "\n") do |tool_version|
      tool = Hash[*tool_version.split(' ')]
      break tool['ruby'] if tool['ruby']
    end

    if ruby_version
      puts "Set ruby version from #{tool_versions_file} file: #{ruby_version}"
      return ruby_version
    end

    puts "No ruby version found in #{tool_versions_file} file, set ruby version to default: #{ruby_default_version}"
  else
    puts "No #{tool_versions_file} file found, set ruby version to default: #{ruby_default_version}"
  end

  ruby_default_version
end