Fix: can't find gem bundler (>= 0.a) with executable bundle (Gem::GemNotFoundException)

When I tried to run bundle install in an environment with multiple Ruby versions managed by rbenv, I hit the following error.

can't find gem bundler (>= 0.a) with executable bundle (Gem::GemNotFoundException)

• The Ruby version was correct,
• the Gemfile was there,
• and I had run gem install bundler so bundle existed too ← this was the problem

yet I still got the error.

I kept getting stuck on this, so I took some notes for future reference.

Conclusion

It was caused by the bundler version (2.0.2) differing from the one in Gemfile.lock (1.17.1).

• The bundler installed via gem was 2.0.2

$ gem install bundler

Successfully installed bundler-2.0.2
Parsing documentation for bundler-2.0.2
Done installing documentation for bundler after 2 seconds
1 gem installed

• The bundler in Gemfile.lock was 1.17.1

...
 VERSION
   ruby 2.5.3p105

BUNDLED WITH
   1.17.1

So once I matched the bundle version being executed to the one in Gemfile.lock, it ran fine.

Fix

$ gem install bundler -v 1.17.1
$ gem uninstall bundler -v 2.0.2

At first glance, (>= 0.a) made me go “huh?”, and thinking “wait, I did set it up though…” is exactly how you get stuck. This was something I wanted to be able to recognize the moment I see this error message.

That’s all.
I hope you find it helpful.