Of Mise and Men

I just tried to build this website with Ruby 4. Bundler refused. The github-pages gem requires Ruby 2.6 or newer, but lower than Ruby 4.

Downgrading Ruby across my Mac would fix one project and risk breaking another. Mise offers a better way. It manages language versions per project without touching the runtimes installed elsewhere on the Mac.

As Stanley Ulili writes in a comparison of mise and rbenv:

Rather than learning different commands for rbenv, nvm, pyenv, and other tools, Mise uses consistent syntax across all languages. This reduces the mental overhead of switching between project types.

Install it with Homebrew and activate it in Zsh:

brew install mise
echo 'eval "$(mise activate zsh)"' >> ~/.zshrc
exec zsh

Then choose a Ruby version inside the project:

cd /Users/jan/janbsc4.github.io
mise use ruby@3.3
gem install bundler -v 2.6.3
bundle install
bundle exec jekyll serve

mise use ruby@3.3 records the choice in the project. When I enter this website’s directory, mise selects Ruby 3.3. Other projects can keep using Ruby 4 or any version they need.

Python projects have a second problem. They often need a specific Python version and an isolated set of packages. Mise can manage both. A mise.toml file can contain:

[tools]
python = "3.13"

[env]
_.python.venv = { path = ".venv", create = true }

With mise active, entering that directory selects Python 3.13 and creates or activates .venv. Packages installed there stay separate from other projects. Another directory can use Python 3.12 and its own virtual environment.

Now, I can jump from this website to a Python project without first checking which Ruby or Python my terminal happens to be using. Each project gets what it needs, nice!