例： vendor/bundleをパスとしてbundle installしたrailtiesの特定ファイルのパスを確認したい
↓

$ bundle exec gem contents railties | grep rails/commands.rb
/home/yu_uchida/my_app/vendor/bundle/ruby/2.6.0/gems/railties-5.2.4.3/lib/rails/commands.rb

　
　
　
comannds.rbの中身を見たいときは
↓

$ cat `bundle exec gem contents railties | grep rails/commands.rb`
# frozen_string_literal: true

require "rails/command"

aliases = {
  "g"  => "generate",
  "d"  => "destroy",
  "c"  => "console",
  "s"  => "server",
  "db" => "dbconsole",
  "r"  => "runner",
  "t"  => "test"
}

command = ARGV.shift
command = aliases[command] || command

Rails::Command.invoke command, ARGV