Why doesn't the bundle install command work?

Question

$ bundle install

Traceback (most recent call last):
    2: from /usr/local/bin/bundle:23:in `<main>'
    1: from /usr/local/lib/site_ruby/2.5.0/rubygems.rb:308:in `activate_bin_path'
/usr/local/lib/site_ruby/2.5.0/rubygems.rb:289:in `find_spec_for_exe': can't find gem bundler (>= 0.a) with executable bundle (Gem::GemNotFoundException)

$ sudo gem update --system
Updating rubygems-update
Successfully installed rubygems-update-3.2.14
Parsing documentation for rubygems-update-3.2.14
Done installing documentation for rubygems-update after 0 seconds
Parsing documentation for rubygems-update-3.2.14
Done installing documentation for rubygems-update after 0 seconds
Installing RubyGems 3.2.14
Traceback (most recent call last):
    4: from setup.rb:23:in `<main>'
    3: from setup.rb:23:in `require'
    2: from /var/lib/gems/2.5.0/gems/rubygems-update-3.2.14/lib/rubygems.rb:1348:in `<top (required)>'
    1: from /var/lib/gems/2.5.0/gems/rubygems-update-3.2.14/lib/rubygems.rb:1348:in `require'
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:43:in `<top (required)>': uninitialized constant Gem::BasicSpecification (NameError)

Answer 1

Please try command. Thank you.

$ bundle update

Answer 2

$ bundle update

Traceback (most recent call last):
    2: from /usr/local/bin/bundle:23:in `<main>'
    1: from /usr/local/lib/site_ruby/2.5.0/rubygems.rb:308:in `activate_bin_path'
/usr/local/lib/site_ruby/2.5.0/rubygems.rb:289:in `find_spec_for_exe': can't find gem bundler (>= 0.a) with executable bundle (Gem::GemNotFoundException)