How do I change the version of yarn used by my system? - macos

Question

I am running Mac OS X 10.14.6 and I am trying to get the latest version of yarn installed and working on my system.
So I installed it with Homebrew, it tells me that I already have it installed on my system:
$ brew install yarn
Warning: yarn 1.21.1 is already installed and up-to-date
But when I do yarn --version, I get this:
$ yarn --version
[DEPRECATION] The trollop gem has been renamed to optimist and will no longer be supported. Please switch to optimist as soon as possible.
Yarn v0.1.1 2011 Jesper Kjeldgaard
So I try to reinstall it and the following happens:
To reinstall 1.21.1, run `brew reinstall yarn`
Transmit-Live $ yarn --version
[DEPRECATION] The trollop gem has been renamed to optimist and will no longer be supported. Please switch to optimist as soon as possible.
Yarn v0.1.1 2011 Jesper Kjeldgaard
Transmit-Live $ brew reinstall yarn
==> Reinstalling yarn
==> Downloading https://yarnpkg.com/downloads/1.21.1/yarn-v1.21.1.tar.gz
Already downloaded: /Library/Caches/Homebrew/downloads/784c559ca8d97--yarn-v1.21.1.tar.gz
🍺 /usr/local/Cellar/yarn/1.21.1: 14 files, 5MB, built in 8 seconds
Transmit-Live $ yarn --version
[DEPRECATION] The trollop gem has been renamed to optimist and will no longer be supported. Please switch to optimist as soon as possible.
Yarn v0.1.1 2011 Jesper Kjeldgaard
I have also tried brew switch and that doesn't work:
$ brew switch yarn 1.21.1
Cleaning /usr/local/Cellar/yarn/1.21.1
2 links created for /usr/local/Cellar/yarn/1.21.1
Transmit-Live $ yarn --version
[DEPRECATION] The trollop gem has been renamed to optimist and will no longer be supported. Please switch to optimist as soon as possible.
Yarn v0.1.1 2011 Jesper Kjeldgaard
Edit 1
I even tried to do brew upgrade yarn and it is the same issue:
$ brew upgrade yarn
Warning: yarn 1.21.1 already installed
Transmit-Live $ yarn --version
[DEPRECATION] The trollop gem has been renamed to optimist and will no longer be supported. Please switch to optimist as soon as possible.
Yarn v0.1.1 2011 Jesper Kjeldgaard
Edit 2
Output of which yarn:
$ which yarn
/.rvm/gems/ruby-2.7.0#myapp/bin/yarn
How do I fix this?
Thanks.

Answer 1

I figured it out.
Basically what was happening is that I had two versions of yarn installed. One was a gem, and the other was the yarn executable.
So I simply ran gem uninstall yarn and it fixed it.
$ gem uninstall yarn
Remove executables:
yarn
in addition to the gem? [Yn] Y
Removing yarn
Successfully uninstalled yarn-0.1.1
Now when I do yarn --version it works properly.
$ yarn --version
1.21.1

Answer 2

You can upgrade a package with brew upgrade, so something like
brew upgrade yarn
You may need to get homebrew to update it's package list first, with brew update
[Edit]
In your case there is some confusion, the yarn package that brew installs is the javascript package manager, whereas the yarn you have on your path is the ruby gem. You can upgrade the latter with gem update yarn. If you want to use the JavaScript package manager, try modifying your path, or use the fully qualified path (something like /use/local/bin/yarn)