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gem Backend ​

The gem backend installs Ruby command-line applications from RubyGems into separate tool directories. Keep application gems in your project's Gemfile and install them with Bundler. The code for this is inside of the mise repository at ./src/backend/gem.rs.

Dependencies ​

This backend needs Ruby and its gem command. Gems with native extensions also need the compiler and libraries required by that gem.

Usage ​

Declare Ruby and RuboCop in the same project:

sh
mise use [email protected] gem:rubocop
mise exec -- rubocop --version

This writes both entries to mise.toml. Add -g for global configuration.

toml
[tools]
ruby = "3.4"
"gem:rubocop" = "latest"

mise's wrappers set GEM_HOME for the selected tool. A RuboCop configuration that uses project-specific plugins may be better run with bundle exec rubocop from a Gemfile that declares those plugins.

Ruby upgrades ​

If the Ruby version used by a gem package changes (whether managed by mise or the system), you may need to reinstall the gem. This can be done with:

sh
mise install -f gem:rubocop

Reinstall under the Ruby version you intend to use. On Unix, mise-managed Ruby shebangs follow a minor-version path so patch upgrades can keep working; moving to another minor version or changing native-extension compatibility can still require a reinstall.

Settings ​

Set these with mise settings set [VARIABLE]=[VALUE] or by setting the environment variable listed.

No settings available.

Tool Options ​

The following tool-options are available for the gem backend—these go in [tools] in mise.toml.

install_env ​

Set environment variables for the gem install command. For gems that build native extensions, MAKEFLAGS controls parallel make jobs:

toml
[tools]
"gem:rubocop" = { version = "latest", install_env = { MAKEFLAGS = "-j4" } }

source ​

Install and resolve versions of one gem from a specific registry, without changing the machine's gem sources:

toml
[tools]
"gem:internal-cli" = { version = "latest", source = "https://{{ env.GEM_TOKEN }}@gems.example.com/acme" }

Private registries take credentials as basic auth in the URL (token@host or user:token@host, per your registry). mise redacts them from output and install metadata. A source with credentials must use https unless it is on localhost.

An https source on rubygems.pkg.github.com without credentials uses mise's GitHub token (see mise token github). It needs read:packages, which a default gh auth login lacks (gh auth refresh -s read:packages). GitHub Packages can't list versions, so pin one:

toml
[tools]
"gem:internal-cli" = { version = "1.4.2", source = "https://rubygems.pkg.github.com/acme" }

The source is added to the other sources rather than replacing them, so dependencies still resolve from rubygems.org, and so can a public gem with the same name. Prefer a registry that proxies rubygems.org, or pin an exact version.

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