# install bundler in user space 
gem install bundler --user-install

# then add following lines to ~/.zshrc on Catalina or ~/.bash_profile on older:
# - to set default bundle install directory
export BUNDLE_PATH=$(ls -t -U | ruby -e 'puts Gem.user_dir')

# - to add user gem directory to $PATH
export PATH="$PATH:$BUNDLE_PATH/bin"