Per Using multiple Bundler versions, https://github.com/rbenv/rbenv/issues/235, et. al. using underscores around the version number should allow me to use different bundler versions on my machine. However, this is not working for me.
When I specify a bundler version that I don't have installed bundler correctly complains though, so it seems to be version checking at least.
$ gem list bundler
*** LOCAL GEMS ***
bundler (2.0.2, 1.17.3, 1.17.0)
$ bundle _1.17.3_ -v
Bundler version 2.0.2
$ bundle _1.17.2_ -v
/Users/user/.rbenv/versions/2.3.6/lib/ruby/2.3.0/rubygems.rb:241:in `bin_path': can't find gem bundler (= 1.17.2) (Gem::GemNotFoundException)
from /Users/user/.rbenv/versions/2.3.6/bin/bundle:22:in `<main>'
I'm seeing this on OS X Mojave 10.14.6, but not running the same experiment on Ubuntu.
I'm looking for suggestions on debugging this.