Setup Jekyll on macOS with brew and rbenv - See https://jekyllrb.com/docs/installation/macos/

README.md

First, make sure you have command line tools installed:

xcode-select --install

Then open Terminal.app and type:

curl https://gist.githubusercontent.com/DirtyF/5d2bde5c682101b7b5d90708ad333bf3/raw/fbc736fa1b50bd637929a315e6803df306c8bc8e/setup-rbenv.sh | bash

setup-rbenv.sh

#!/bin/bash

set -ex

brew update
brew install rbenv ruby-build

rbenv install 2.6.5

echo "export GEM_HOME=$HOME/gems" >> ~/.zshrc
echo "export PATH=$HOME/gems/bin:$PATH" >> ~/.zshrc
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.zshrc

if ! type rbenv | grep function; then
  echo 'if which rbenv > /dev/null; then eval "$(rbenv init -)"; fi' >> ~/.zshrc
fi

source ~/.zshrc

curl -fsSL https://github.com/rbenv/rbenv-installer/raw/master/bin/rbenv-doctor | bash
rbenv global 2.6.5

gem install jekyll bundler
rbenv rehash
ruby -v
jekyll -v

set +x
echo "Done! Close and reopen your terminal"

I just ran the commands in setup-rbenv.sh, but it turns out that we should run the following command(from this answer on stackoverflow) after installing rbenv in order to make rbenv global 2.4.3 work:

# for bash:
$ echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bash_profile
$ echo 'eval "$(rbenv init -)"' >> ~/.bash_profile
# for zsh:
$ echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.zshrc
$ echo 'eval "$(rbenv init -)"' >> ~/.zshrc

Then reopen terminal.
Or the version of ruby would still be the one pre-installed on macos.

I have rbenv global 2.5.3 but still unable to use the command jekyll serve
Please help.