INSTALL_COSMOS.bat for COSMOS v4 no longer works

[YungCorn]

The INSTALL_COSMOS.bat install script for Windows 7+ no longer works. The version of the script is 2.6, and I downloaded it from here: https://ballaerospace.github.io/cosmos-website/docs/v4/installation. I know COSMOS v4 is no longer being officially supported, but I thought I'd still open this issue just in case.

When running the script, this is the error I encountered:

Updating rubygems-update
Fetching: rubygems-update-3.4.12.gem (100%)
ERROR:  Error installing rubygems-update:
        There are no versions of rubygems-update (= 3.4.12) compatible with your Ruby & RubyGems
        rubygems-update requires Ruby version >= 2.6.0. The current ruby version is 2.5.0.
ERROR:  While executing gem ... (NoMethodError)
    undefined method `version' for nil:NilClass
Installing COSMOS gem "LATEST"...
Fetching: bundler-2.4.12.gem (100%)
ERROR:  Error installing cosmos:
        The last version of bundler (>= 1.3) to support your Ruby & RubyGems was 2.3.26. Try installing it with `gem install bundler -v 2.3.26` and then running the current command again
        bundler requires Ruby version >= 2.6.0. The current ruby version is 2.5.0.
ERROR: Problem installing cosmos gem
INSTALL FAILED
Press any key to continue . . .

It should be very easy to recreate this error. Simply try running the install script on a computer which doesn't already have COSMOS v4 installed on it.

I was able to get around the problem by modifying the INSTALL_COSMOS.bat file. I replaced this line:
call gem update --system
with the following:
call gem install bundler -v 2.3.26

The install appears to have worked with that change, in case anyone is looking for a quick fix.