First, check the version of Ruby you are using.
$ruby -v
ruby
2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-darwin18]
$ which ruby
usr/bin/ruby
Now use Homebrew to install the latest Ruby.
$ brew install ruby
==> ruby
By default, binaries installed by gem will be placed into:
/usr/local/lib/ruby/gems/2.7.0/bin
You may want to add this to your PATH.
ruby is keg-only, which means it was not symlinked into /usr/local,
because macOS already provides this software and installing another version in
parallel can cause all kinds of trouble.
If you need to have ruby first in your PATH run:
$ echo 'export PATH="/usr/local/opt/ruby/bin:$PATH"' >> /Users/xxx/.bash_profile
(For newer mac the file name will be : .zprofile )
For compilers to find ruby you may need to set:
$ export LDFLAGS="-L/usr/local/opt/ruby/lib"
$ export CPPFLAGS="-I/usr/local/opt/ruby/include"
Follow the instructions to set PATH. Now you will go to see the installed Ruby. Make sure to replace the 'xxx' with your username.
$ echo 'export PATH="/usr/local/opt/ruby/bin:$PATH"' >> /Users/xxx/.bash_profile
$ echo 'export LDFLAGS="-L/usr/local/opt/ruby/lib"' >> ~/.bash_profile
$ echo 'export CPPFLAGS="-I/usr/local/opt/ruby/include"' >> ~/.bash_profile
$ source ~/.bash_profile
(For newer mac the file name will be : .zprofile )
Finally, Make sure your PATH is in place.
$ ruby -v
ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-darwin18]
$ which ruby
/usr/local/opt/ruby/bin/ruby
You're good to go! Make sure you install by specifying the save destination as follows.
$ sudo gem install -n /usr/local/bin cocoapods