> ruby-build mostly does not verify that system dependencies are present before downloading and attempting to compile Ruby from source. Please ensure that [all requisite libraries][build-env] such as build tools and development headers are already present on your system.
Basically, what ruby-build does when installing a Ruby version is this:
- Downloads an official tarball of Ruby source code;
- Extracts the archive into a temporary directory on your system;
- Executes `./configure --prefix=/path/to/destination` in the source code;
- Runs `make install` to compile Ruby;
- Verifies that the installed Ruby is functional.
Depending on the context, ruby-build does a little bit more than the above: for example, it will try to link Ruby to the appropriate OpenSSL version, even if that means downloading and compiling OpenSSL itself; it will discover and link to Homebrew-installed instances of some libraries like libyaml and readline, etc.
When listing "latest" Ruby versions, such as in `ruby-build --list` output, ruby-build only knows of Ruby versions that are bundled with this project. That means that when a new Ruby version comes out, ruby-build will not know about it immediately— you will have to upgrade ruby-build before you can use it to install the new Ruby version. This is because ruby-build bundles [definition files](#custom-build-definitions) for each individual Ruby version.
If it's important to you that your installer tool always consults remote resources to download the list of latest Ruby versions (without having to upgrade the tool itself), check out [ruby-install][] as an alternative to ruby-build.
### Ruby implementations
ruby-build ships with definitions for the following Ruby implementations, denoted by version prefixes in the `ruby-build --list` output:
- [CRuby][]: listed in ruby-build as unprefixed version numbers in the `X.Y.Z` format. This is the main Ruby implementation that most people use and is also historically known as "MRI". ruby-build allows adding the `ruby-` prefix to CRuby version numbers for compatibility with other version managers.
-`jruby`: [JRuby][] is a high-performance Ruby implementation with real threading built on top of the Java virtual machine (JVM).
-`mruby`: [mruby][] is a lightweight, embeddable Ruby implementation for microcontrollers.
-`picoruby`: [PicoRuby][] is an alternative mruby implementation for one-chip microcontrollers.
-`truffleruby`: The Native standalone distribution of [TruffleRuby][], an implementation of Ruby on top of GraalVM's Truffle framework.
-`truffleruby+graalvm`: The JVM standalone distribution of TruffleRuby.
To install a version of Ruby that is not available in ruby-build, you can specify the path to a custom build definition file in place of a Ruby version number.
```sh
# As a standalone program
$ ruby-build -d /path/to/3.4-custom /opt/rubies # installs to /opt/rubies/3.4-custom
# As an rbenv plugin
$ rbenv install /path/to/3.4-custom # installs to $(rbenv root)/versions/3.4-custom
```
You can also provide a _directory_ of custom build definition files.
The path(s) will be searched along with ruby-build's bundled `share/ruby-build/` directory.
(Perhaps a collection of 3rd-party build definitions published as a git repo,
or an organization's custom build definitions distributed in-house.)
```sh
# As a standalone program
$ RUBY_BUILD_DEFINITIONS=/path/to/custom/defs ruby-build --definitions # lists all available versions of Ruby, including custom defs
$ RUBY_BUILD_DEFINITIONS=/path/to/custom/defs ruby-build -d 3.5-custom /opt/rubies # installs to /opt/rubies/3.5-custom
# As an rbenv plugin
$ RUBY_BUILD_DEFINITIONS=/path/to/custom/defs rbenv install --list # lists all available versions of Ruby, including custom defs
$ RUBY_BUILD_DEFINITIONS=/path/to/custom/defs rbenv install 3.5-custom # installs to $(rbenv root)/versions/3.5-custom
Both `rbenv install` and `ruby-build` commands support the `-p/--patch` flag to apply a patch to the Ruby source code before building. Patches are read from standard input:
All Ruby definition files bundled with ruby-build include checksums for packages, meaning that all externally downloaded packages are automatically checked for integrity after fetching.
