gem update on Mac High Sierra throwing Operation not permitted @ rb_sysopen error

Question

I am having some permissions problems with Sass on my mac with High Sierra. If I try sudo gem update --system I get the following:

Updating rubygems-update
Fetching: rubygems-update-2.7.4.gem (100%)
Successfully installed rubygems-update-2.7.4
Parsing documentation for rubygems-update-2.7.4
Installing ri documentation for rubygems-update-2.7.4
Installing darkfish documentation for rubygems-update-2.7.4
Done installing documentation for rubygems-update after 44 seconds
Parsing documentation for rubygems-update-2.7.4
Done installing documentation for rubygems-update after 0 seconds
Installing RubyGems 2.7.4
ERROR:  While executing gem ... (Errno::EPERM)
    Operation not permitted @ rb_sysopen - /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/gem

Answer 1

Interestingly gem update --system works without any problems.