rtx

Polyglot runtime manager

Quickstart (macOS)

Install rtx (other methods here):

$ brew install jdxcode/tap/rtx
$ rtx --version
rtx 1.0.1

Hook rtx into to your shell (choose one, and open a new shell session for the changes to take effect):

$ echo 'eval "$(rtx activate -s bash)"' >> ~/.bashrc
$ echo 'eval "$(rtx activate -s zsh)"' >> ~/.zshrc
$ echo 'rtx activate -s fish | source' >> ~/.config/fish/config.fish

Install a runtime and set it as the default:

$ rtx install nodejs@18
$ rtx global nodejs@18
$ node -v
v18.10.9

Note
rtx install is optional, rtx global will prompt to install the runtime if it's not already installed. This is configurable in ~/.config/rtx/config.toml.

About

rtx is a tool for managing programming language and tool versions. For example, use this to install a particular version of node.js and ruby for a project. Using rtx activate, you can have your shell automatically switch to the correct node and ruby versions when you cd into the project's directory. Other projects on your machine can use a different set of versions.

rtx is inspired by asdf and uses asdf's vast plugin ecosystem under the hood. However, it is much faster than asdf and has a more friendly user experience. For more on how rtx compares to asdf, see below. The goal of this project was to create a better front-end to asdf.

It uses the same .tool-versions file that asdf uses. It's also compatible with idiomatic version files like .node-version but you need to enable "legacy version file support" in the config.

How it works

rtx installs as a shell extension (e.g. rtx activate -s zsh) that sets the PATH environment variable to point your shell to the correct runtime binaries. When you cd into a directory containing a .tool-versions file, rtx will automatically activate the correct versions.

Every time your prompt starts it will call rtx hook-env to fetch new environment variables. This should be very fast and it exits early if the the directory wasn't changed or the .tool-version files haven't been updated. On my machine this takes 1-2ms even if it doesn't exit early.

Unlike asdf which uses shim files to dynamically locate runtimes when they're called, rtx modifies PATH ahead of time so the runtimes are called directly. This is not only faster since it avoids any overhead, but it also makes it so commands like which node work as expected. This also means there isn't any need to run asdf reshim after installing new runtime binaries.

Common example commands

rtx install nodejs@20.0.0       Install a specific version number
rtx install nodejs@20.0         Install a fuzzy version number
rtx local nodejs@20             Use node-20.x in current project
rtx global nodejs@20            Use node-20.x as default

rtx install nodejs              Install the latest available version
rtx local nodejs@latest         Use latest node in current directory
rtx global nodejs@system        Use system node as default

rtx x nodejs@20 -- node app.js  Run `node app.js` with the PATH pointing to node-20.x

Installation

Warning Regardless of the installation method, when uninstalling rtx, remove RTX_DATA_DIR folder (usually ~/.local/share/rtx) to fully clean up.

Standalone

Note that it isn't necessary for rtx to be on PATH. If you run the activate script in your rc file, rtx will automatically add itself to PATH.

$ curl https://rtx.jdxcode.com/install.sh | sh

Homebrew

$ brew install jdxcode/tap/rtx

Cargo

Build from source with Cargo.

$ cargo install rtx-cli

Do it faster with cargo-binstall:

$ cargo install cargo-binstall
$ cargo binstall rtx-cli

npm

rtx is available on npm as precompiled binaries. This isn't a node.js package, just distributed via npm. It can be useful for JS projects that want to setup rtx via package.json or npx.

$ npm install -g @jdxcode/rtx

Or use npx if you just want to test it out for a single command without fully installing:

$ npx @jdxcode/rtx exec python@3.11 -- python some_script.py

GitHub Releases

Download the latest release from GitHub.

$ curl https://github.com/jdxcode/rtx/releases/rtx-latest-macos-arm64.tar.xz | tar -xJv
$ mv rtx/bin/rtx /usr/local/bin

apt (coming soon)

For installation on Ubuntu/Debian:

wget -qO - https://rtx.jdxcode.com/gpg-key.pub | gpg --dearmor | sudo tee /usr/share/keyrings/rtx-archive-keyring.gpg 1> /dev/null
echo "deb [signed-by=/usr/share/keyrings/rtx-archive-keyring.gpg arch=amd64] https://rtx.jdxcode.com/deb stable main" | sudo tee /etc/apt/sources.list.d/rtx.list
sudo apt update
sudo apt install -y rtx

Warning If you're on arm64 you'll need to run the following: echo "deb [signed-by=/usr/share/keyrings/rtx-archive-keyring.gpg arch=arm64] https://rtx.jdxcode.com/deb stable main" | sudo tee /etc/apt/sources.list.d/rtx.list

dnf (coming soon)

For Fedora, CentOS, Amazon Linux, RHEL and other dnf-based distributions:

dnf install -y dnf-plugins-core
dnf config-manager --add-repo https://rtx.jdxcode.com/rpm/rtx.repo
dnf install -y rtx

yum (coming soon)

yum install -y yum-utils
yum config-manager --add-repo https://rtx.jdxcode.com/rpm/rtx.repo
yum install -y rtx

apk (coming soon)

For Alpine Linux:

apk add rtx --repository=http://dl-cdn.alpinelinux.org/alpine/edge/testing/

aur (coming soon)

For Arch Linux:

git clone https://aur.archlinux.org/rtx.git
cd rtx
makepkg -si

Other Shells

Bash

$ echo 'eval "$(rtx activate -s bash)"' >> ~/.bashrc

Fish

$ echo 'rtx activate -s fish | source' >> ~/.config/fish/config.fish

Configuration

.tool-versions

The .tool-versions file is used to specify the runtime versions for a project. An example of this is:

nodejs      20.0.0  # comments are allowed
ruby        3       # can be fuzzy version
shellcheck  latest  # also supports "latest"
jq          1.6

Create .tool-versions files manually, or use rtx local to create them automatically. See the asdf docs for more info on this file format.

Global config: ~/.config/rtx/config.toml

rtx can be configured in ~/.config/rtx/config.toml. The following options are available (defaults shown):

# whether to prompt to install plugins and runtimes if they're not already installed
missing_runtime_behavior = 'prompt' # other options: 'ignore', 'warn', 'prompt', 'autoinstall'

# plugins can read the versions files used by other version managers (if enabled by the plugin)
# for example, .nvmrc in the case of nodejs's nvm
legacy_version_file = false         # not enabled by default

# configure `rtx install` to always keep the downloaded archive
always_keep_download = false        # deleted after install by default

# configure how frequently (in minutes) to fetch updated plugin repository changes
# this is updated whenever a new runtime is installed
plugin_autoupdate_last_check_duration = 10080 # (one week) set to 0 to disable updates

# configure how frequently (in minutes) to fetch updated shortname repository changes
# note this is not plugins themselves, it's the shortname mappings
# e.g.: nodejs -> https://github.com/asdf-vm/asdf-nodejs.git
plugin_repository_last_check_duration = 10080 # (one week) set to 0 to disable updates

# disables the short name repository (described above)
disable_plugin_short_name_repository = false

[alias.nodejs]
my_custom_node = '18'  # makes `rtx install nodejs@my_custom_node` install node-18.x
                       # this can also be specified in a plugin (see below in "Aliases")

Environment variables

rtx can also be configured via environment variables. The following options are available:

RTX_MISSING_RUNTIME_BEHAVIOR

This is the same as the missing_runtime_behavior config option in ~/.config/rtx/config.toml.

RTX_DATA_DIR

This is the directory where rtx stores its data. The default is ~/.local/share/rtx.

$ RTX_MISSING_RUNTIME_BEHAVIOR=ignore rtx install nodejs@20
$ RTX_NODEJS_VERSION=20 rtx exec -- node --version

RTX_CONFIG_FILE

This is the path to the config file. The default is ~/.config/rtx/config.toml. (Or $XDG_CONFIG_HOME/config.toml if that is set)

RTX_DEFAULT_TOOL_VERSIONS_FILENAME

Set to something other than ".tool-versions" to have rtx look for configuration with alternate names.

RTX_${PLUGIN}_VERSION

Set the version for a runtime. For example, RTX_NODEJS_VERSION=20 will use nodejs@20.x regardless of what is set in .tool-versions.

RTX_LEGACY_VERSION_FILE

Plugins can read the versions files used by other version managers (if enabled by the plugin) for example, .nvmrc in the case of nodejs's nvm.

Aliases

rtx supports aliasing the versions of runtimes. One use-case for this is to define aliases for LTS versions of runtimes. For example, you may want to specify lts/hydrogen as the version for nodejs@18.x. So you can use the runtime with nodejs lts/hydrogen in .tool-versions.

User aliases can be created by adding an alias.<PLUGIN> section to ~/.config/rtx/config.toml:

[alias.nodejs]
my_custom_18 = '18'

Plugins can also provide aliases via a bin/list-aliases script. Here is an example showing node.js versions:

#!/usr/bin/env bash

echo "lts/hydrogen 18"
echo "lts/gallium 16"
echo "lts/fermium 14"

Note: Because this is rtx-specific functionality not currently used by asdf it isn't likely to be in any plugin currently, but plugin authors can add this script without impacting asdf users.

Plugins

rtx uses asdf's plugin ecosystem under the hood. See https://github.com/asdf-vm/asdf-plugins for a list.

FAQs

I don't want to put a .tool-versions file into my project since git shows it as an untracked file.

You can make git ignore these files in 3 different ways:

• Adding .tool-versions to project's .gitignore file. This has the downside that you need to commit the change to the ignore file.
• Adding .tool-versions to project's .git/info/exclude. This file is local to your project so there is no need to commit it.
• Adding .tool-versions to global gitignore (core.excludesFile). This will cause git to ignore .tool-versions files in all projects. You can explicitly add one to a project if needed with git add --force .tool-versions.

How do I create my own plugin?

Just follow the asdf docs. Everything should work the same. If it isn't, please open an issue.

rtx is failing or not working right

First try setting RTX_LOG_LEVEL=debug or RTX_LOG_LEVEL=trace and see if that gives you more information. You can also set RTX_LOG_FILE=/path/to/logfile to write the logs to a file.

If something is happening with the activate hook, you can try disabling it and calling eval "$(rtx hook-env)" manually. It can also be helpful to use rtx env to see what environment variables it wants to use.

Lastly, there is an rtx doctor command. It doesn't have much in it but I hope to add more functionality to that to help debug issues.

Windows support?

This is unlikely to ever happen since this leverages the vast ecosystem of asdf plugins which are built on Bash scripts. At some point it may be worth exploring an alternate plugin format that would be Windows compatible.

Commands

rtx activate

Enables rtx to automatically modify runtimes when changing directory

This should go into your shell's rc file. Otherwise it will only
take effect in the current session.
(e.g. ~/.bashrc)

Usage: activate [OPTIONS]

Options:
  -s, --shell <SHELL>
          Shell type to generate script for
          
          [possible values: bash, fish, zsh]

  -h, --help
          Print help (see a summary with '-h')


Examples:
    $ eval "$(rtx activate -s bash)"
    $ eval "$(rtx activate -s zsh)"
    $ rtx activate -s fish | source

rtx alias ls

List aliases
Shows the aliases that can be specified.
These can come from user config or from plugins in `bin/list-aliases`.

For user config, aliases are defined like the following in `~/.config/rtx/config.toml`:

  [aliases.nodejs]
  lts = "18.0.0"

Usage: ls [OPTIONS]

Options:
  -p, --plugin <PLUGIN>
          Show aliases for <PLUGIN>

  -h, --help
          Print help (see a summary with '-h')

Examples:
  $ rtx aliases
  nodejs    lts/hydrogen   18.0.0

rtx deactivate

disable rtx for current shell session

This can be used to temporarily disable rtx in a shell session.

Usage: deactivate [OPTIONS]

Options:
  -s, --shell <SHELL>
          shell type to generate the script for
          
          e.g.: bash, zsh, fish
          
          [possible values: bash, fish, zsh]

  -h, --help
          Print help (see a summary with '-h')


Examples:
    $ eval "$(rtx deactivate -s bash)"
    $ eval "$(rtx deactivate -s zsh)"
    $ rtx deactivate -s fish | source

rtx doctor

Check rtx installation for possible problems.

Usage: doctor

Options:
  -h, --help
          Print help (see a summary with '-h')


Examples:
  $ rtx doctor
  [WARN] plugin nodejs is not installed

rtx env

exports environment variables to activate rtx in a single shell session

It's not necessary to use this if you have `rtx activate` in your shell rc file.
Use this if you don't want to permanently install rtx.
This can be used similarly to `asdf shell`.
Unfortunately, it requires `eval` to work since it's not written in Bash though.
It's also useful just to see what environment variables rtx sets.

Usage: env [OPTIONS] [RUNTIME]...

Arguments:
  [RUNTIME]...
          runtime version to use

Options:
  -s, --shell <SHELL>
          Shell type to generate environment variables for
          
          [possible values: bash, fish, zsh]

  -h, --help
          Print help (see a summary with '-h')


Examples:
  $ eval "$(rtx env -s bash)"
  $ eval "$(rtx env -s zsh)"
  $ rtx env -s fish | source

rtx exec

execute a command with runtime(s) set

use this to avoid modifying the shell session or running ad-hoc commands with the rtx runtimes
set.

Runtimes will be loaded from .tool-versions, though they can be overridden with <RUNTIME> args
Note that only the plugin specified will be overriden, so if a `.tool-versions` file
includes "nodejs 20" but you run `rtx exec python@3.11`; it will still load nodejs@20.

The "--" separates runtimes from the commands to pass along to the subprocess.

Usage: exec [OPTIONS] [RUNTIME]... [-- <COMMAND>...]

Arguments:
  [RUNTIME]...
          runtime(s) to start
          
          e.g.: nodejs@20 python@3.10

  [COMMAND]...
          the command string to execute (same as --command)

Options:
  -c, --command <C>
          the command string to execute

  -h, --help
          Print help (see a summary with '-h')


Examples:
  rtx exec nodejs@20 -- node ./app.js  # launch app.js using node-20.x
  rtx x nodejs@20 -- node ./app.js     # shorter alias

Specify command as a string:
  rtx exec nodejs@20 python@3.11 --command "node -v && python -V"

rtx global

sets global .tool-versions to include a specified runtime

this file is `$HOME/.tool-versions` by default
use `rtx local` to set a runtime version locally in the current directory

Usage: global [OPTIONS] [RUNTIME]...

Arguments:
  [RUNTIME]...
          runtimes
          
          e.g.: nodejs@20

Options:
      --fuzzy
          save fuzzy match to .tool-versions e.g.: `rtx global --fuzzy nodejs@20` will save `nodejs 20` to .tool-versions, by default, it would save the exact version, e.g.: `nodejs 20.0.0`

      --remove <PLUGIN>
          remove the plugin(s) from ~/.tool-versions

  -h, --help
          Print help (see a summary with '-h')


Examples:
  # set the current version of nodejs to 20.x
  # will use a precise version (e.g.: 20.0.0) in .tool-versions file
  $ rtx global nodejs@20     

  # set the current version of nodejs to 20.x
  # will use a fuzzy version (e.g.: 20) in .tool-versions file
  $ rtx global --fuzzy nodejs@20

rtx install

install a runtime

this will install a runtime to `~/.local/share/rtx/installs/<PLUGIN>/<VERSION>`
it won't be used simply by being installed, however.
For that, you must set up a `.tool-version` file manually or with `rtx local/global`.
Or you can call a runtime explicitly with `rtx exec <PLUGIN>@<VERSION> -- <COMMAND>`.

Usage: install [OPTIONS] [RUNTIME]...

Arguments:
  [RUNTIME]...
          runtime(s) to install
          
          e.g.: nodejs@20

Options:
  -p, --plugin <PLUGIN>
          only install runtime(s) for <PLUGIN>

  -f, --force
          force reinstall even if already installed

  -h, --help
          Print help (see a summary with '-h')


Examples:
  $ rtx install nodejs@18.0.0  # install specific nodejs version
  $ rtx install nodejs@18      # install fuzzy nodejs version
  $ rtx install nodejs         # install latest nodejs version—or what is specified in .tool-versions
  $ rtx install                # installs all runtimes specified in .tool-versions for installed plugins

rtx latest

get the latest runtime version of a plugin's runtimes

Usage: latest <RUNTIME>

Arguments:
  <RUNTIME>
          Runtime to get the latest version of

Options:
  -h, --help
          Print help (see a summary with '-h')


Examples:
  $ rtx latest nodejs@18  # get the latest version of nodejs 18
  18.0.0
  
  $ rtx latest nodejs     # get the latest stable version of nodejs
  20.0.0

rtx local

Sets .tool-versions to include a specific runtime

use this to set the runtime version when within a directory
use `rtx global` to set a runtime version globally

Usage: local [OPTIONS] [RUNTIME]...

Arguments:
  [RUNTIME]...
          runtimes to add to .tool-versions
          
          e.g.: nodejs@20

Options:
  -p, --parent
          recurse up to find a .tool-versions file rather than using the current directory only by default this command will only set the runtime in the current directory ("$PWD/.tool-versions")

      --fuzzy
          save fuzzy match to .tool-versions e.g.: `rtx local --fuzzy nodejs@20` will save `nodejs 20` to .tool-versions by default it would save the exact version, e.g.: `nodejs 20.0.0`

      --remove <PLUGIN>
          remove the plugin(s) from .tool-versions

  -h, --help
          Print help (see a summary with '-h')


Examples:
  # set the current version of nodejs to 20.x for the current directory
  # will use a precise version (e.g.: 20.0.0) in .tool-versions file
  $ rtx local nodejs@20

  # set nodejs to 20.x for the current project (recurses up to find .tool-versions)
  $ rtx local -p nodejs@20

  # set the current version of nodejs to 20.x for the current directory
  # will use a fuzzy version (e.g.: 20) in .tool-versions file
  $ rtx local --fuzzy nodejs@20

  # removes nodejs from .tool-versions
  $ rtx local --remove=nodejs

rtx ls

list installed runtime versions

The "arrow (->)" indicates the runtime is installed, active, and will be used for running commands.
(Assuming `rtx activate` or `rtx env` is in use).

Usage: ls [OPTIONS]

Options:
  -p, --plugin <PLUGIN>
          Only show runtimes from [PLUGIN]

  -c, --current
          Only show runtimes currently specified in .tool-versions

  -h, --help
          Print help (see a summary with '-h')


Examples:
  $ rtx list
  -> nodejs     20.0.0 (set by ~/src/myapp/.tool-versions)
  -> python     3.11.0 (set by ~/.tool-versions)
     python     3.10.0
     
  $ rtx list --current
  -> nodejs     20.0.0 (set by ~/src/myapp/.tool-versions)
  -> python     3.11.0 (set by ~/.tool-versions)

rtx ls-remote

list runtime versions available for install
note that these versions are cached for commands like `rtx install nodejs@latest`
however _this_ command will always clear that cache and fetch the latest remote versions

Usage: ls-remote <PLUGIN>

Arguments:
  <PLUGIN>
          Plugin

Options:
  -h, --help
          Print help (see a summary with '-h')


Examples:
  $ rtx list-remote nodejs
  18.0.0
  20.0.0

rtx plugins install

install a plugin

note that rtx automatically can install plugins when you install a runtime
e.g.: `rtx install nodejs@18` will autoinstall the nodejs plugin

This behavior can be modified in ~/.rtx/config.toml

Usage: install [OPTIONS] <NAME> [GIT_URL]

Arguments:
  <NAME>
          The name of the plugin to install
          
          e.g.: nodejs, ruby

  [GIT_URL]
          The git url of the plugin
          
          e.g.: https://github.com/asdf-vm/asdf-nodejs.git

Options:
  -f, --force
          Reinstalls even if plugin exists

  -h, --help
          Print help (see a summary with '-h')


EXAMPLES:
    $ rtx install nodejs  # install the nodejs plugin using the shorthand repo:
                          # https://github.com/asdf-vm/asdf-plugins

    $ rtx install nodejs https://github.com/asdf-vm/asdf-nodejs.git
                          # install the nodejs plugin using the git url

    $ rtx install https://github.com/asdf-vm/asdf-nodejs.git
                          # install the nodejs plugin using the git url only
                          # (nodejs is inferred from the url)

rtx plugins ls

List installed plugins

Can also show remotely available plugins to install.

Usage: ls [OPTIONS]

Options:
  -a, --all
          list all available remote plugins
          
          same as `rtx plugins ls-remote`

  -u, --urls
          show the git url for each plugin
          
          e.g.: https://github.com/asdf-vm/asdf-nodejs.git

  -h, --help
          Print help (see a summary with '-h')

List installed plugins
Can also show remotely available plugins to install.

Examples:

  $ rtx plugins ls
  nodejs
  ruby
  
  $ rtx plugins ls --urls
  nodejs                        https://github.com/asdf-vm/asdf-nodejs.git
  ruby                          https://github.com/asdf-vm/asdf-ruby.git

rtx plugins ls-remote

List all available remote plugins

These are fetched from https://github.com/asdf-vm/asdf-plugins

Examples:
  $ rtx plugins ls-remote


Usage: ls-remote [OPTIONS]

Options:
  -u, --urls
          show the git url for each plugin
          
          e.g.: https://github.com/asdf-vm/asdf-nodejs.git

  -h, --help
          Print help (see a summary with '-h')

rtx plugins uninstall

removes a plugin

Usage: uninstall <PLUGIN>

Arguments:
  <PLUGIN>
          plugin to remove

Options:
  -h, --help
          Print help (see a summary with '-h')


Examples:
  $ rtx uninstall nodejs

rtx plugins update

updates a plugin to the latest version

note: this updates the plugin itself, not the runtime versions

Usage: update [PLUGIN]...

Arguments:
  [PLUGIN]...
          plugin(s) to update

Options:
  -h, --help
          Print help (see a summary with '-h')


Examples:
  rtx plugins update         # update all plugins
  rtx plugins update nodejs  # update only nodejs

rtx uninstall

removes a runtime version

Usage: uninstall <RUNTIME>...

Arguments:
  <RUNTIME>...
          runtime(s) to remove

Options:
  -h, --help
          Print help (see a summary with '-h')


Examples:
  $ rtx uninstall nodejs

rtx version

Show rtx version

Usage: version

Options:
  -h, --help
          Print help

Comparison to asdf

rtx is mostly a clone of asdf, but there are notable areas where improvements have been made.

Performance

asdf made (what I consider) a poor design decision to use shims that go between a call to a runtime and the runtime itself. e.g.: when you call node it will call an asdf shim file ~/.asdf/shims/node, which then calls asdf exec, which then calls the correct version of node.

These shims have terrible performance, adding ~200ms to every call. rtx does not use shims and instead updates PATH so that it doesn't have any overhead when simply calling binaries. These shims are the main reason that I wrote this.

I don't think it's possible for asdf to fix thse issues. The author of asdf did a great writeup of performance problems. asdf is written in bash which certainly makes it challening to be performant, however I think the real problem is the shim design. I don't think it's possible to fix that without a complete rewrite.

rtx does call an internal command rtx hook-env every time the directory has changed, but because it's written in Rust, this is very quick—taking ~2ms on my machine.

tl;dr: asdf adds overhead (~200ms) when calling a runtime, rtx adds a tiny amount of overhead (~2ms) when changing directories.

Environment variables

asdf only helps manage runtime executables. However, some tools are managed via environment variables (notably Java which switches via JAVA_HOME). This isn't supported very well in asdf and requires a separate shell extension just to manage.

However asdf plugins have a bin/exec-env script that is used for exporting environment variables like JAVA_HOME. rtx simply exports the environment variables from the bin/exec-env script in the plugin but places them in the shell for all commands. In asdf it only exports those commands when the shim is called. This means if you call java it will set JAVA_HOME, but not if you call some Java tool like mvn.

This means we're just using the existing plugin script but because rtx doesn't use shims it can be used for more things. It would be trivial to make a plugin that exports arbitrary environment variables like dotenv or direnv.

UX

Some commands are the same in asdf but others have been changed. Everything that's possible in asdf should be possible in rtx but may use slighly different syntax. rtx has more forgiving commands, such as using fuzzy-matching, e.g.: rtx install nodejs@18. While in asdf you can run asdf install nodejs latest:18, you can't use latest:18 in a .tool-versions file or many other places. In rtx you can use fuzzy-matching everywhere.

asdf requires several steps to install a new runtime if the plugin isn't installed, e.g.:

$ asdf plugin add nodejs
$ asdf install nodejs latest:18
$ asdf local nodejs latest:18

In rtx this can all be done in a single step to set the local runtime version. If the plugin and/or runtime needs to be installed it will prompt:

$ asdf local nodejs@18
rtx: Would you like to install nodejs@18.13.0? [Y/n] Y
Trying to update node-build... ok
Downloading node-v18.13.0-darwin-arm64.tar.gz...
-> https://nodejs.org/dist/v18.13.0/node-v18.13.0-darwin-arm64.tar.gz
Installing node-v18.13.0-darwin-arm64...
Installed node-v18.13.0-darwin-arm64 to /Users/jdx/.local/share/rtx/installs/nodejs/18.13.0
$ node -v
v18.13.0

I've found asdf to be particularly rigid and difficult to learn. It also made strange decisions like having asdf list all but asdf latest --all (why is one a flag and one a positional argument?). rtx makes heavy use of aliases so you don't need to remember if it's rtx plugin add nodejs or rtx plugin install nodejs. asdf also just has too many commands. It's hard to remember what the difference is between asdf list and asdf current is. rtx has a single command rtx list which can be passed a flag rtx list --current to show the current versions.

That said, there are a lot of great things about asdf. It's the best multi-runtime manager out there and I've really been impressed with the plugin system. Most of the design decisions the authors made were very good. I really just have 2 complaints: the shims and the fact it's written in Bash.

Cache Behavior

rtx makes use of caching in many places in order to be efficient. The details about how long to keep cache for should eventually all be configurable. There may be gaps in the current behavior where things are hardcoded but I'm happy to add more settings to cover whatever config is needed.

Below I explain the behavior it uses around caching. If you're seeing behavior where things don't appear to be updating, this is a good place to start.

Shorthand Repository Cache

asdf maintains a shorthand repository which maps plugin short names (e.g.: nodejs) to full repository names (e.g.: https://github.com/asdf-vm/asdf-nodejs).

This is stored in ~/.local/share/rtx/repository and updated every week by default if short names are requested. This is similar to what asdf does, but I'm considering just baking this straight into the codebase so it doesn't have to be fetched/maintained separately. It's not like new plugins get added that often.

Plugin Cache

Each plugin has a cache that's stored in ~/.local/share/rtx/plugins/<PLUGIN>/.rtxcache.msgpack.gz. It stores the list of versions available for that plugin (rtx ls-remote <PLUGIN>) and the legacy filenames (see below).

It is updated daily by default or anytime that rtx ls-remote is called explicitly. The file is gzipped messagepack, if you want to view it you can run the following (requires msgpack-cli).

cat ~/.local/share/rtx/plugins/nodejs/.rtxcache.msgpack.gz | gunzip | msgpack-cli decode

Runtime Cache

Each runtime (language version, e.g.: nodejs@20.0.0), has a file called "runtimeconf" that's stored inside the install directory, e.g.: ~/.asdf/installs/nodejs/20.0.0/.rtxconf.msgpack. This stores the information about the runtime that should not change after installation. Currently this is just the bin paths the plugin defines in bin/list-bin-paths. By default this is just /bin. It's the list of paths that rtx will add to PATH when the runtime is activated.

I have not seen a plugins which has dynamic bin paths but let me know if you find one. If that is the case, we may need to make this cached instead of static.

"Runtimeconf" is stored as uncompressed messagepack and can be viewed with the following:

cat ~/.local/share/rtx/installs/nodejs/18.13.0/.rtxconf.msgpack | msgpack-cli decode

Legacy File Cache

If enabled with legacy_version_file = true in ~/.config/rtx/config.toml, rtx will read the legacy filenames such as .node-version for asdf-nodejs. This leverages cache in 2 places where the plugin is called:

• list-legacy-filenames In every plugin I've seen this simply returns a static list of filenamed like ".nvmrc .node-version". It's cached alongside the standard "runtime" cache which is refreshed daily by default.
• parse-legacy-file This plugin binary is called to parse a legacy file to get the version out of it. It's relatively expensive so every file that gets parsed as a legacy file is cached into ~/.local/share/rtx/legacy_cache. It will remain cached until the file is modified. This is a simple text file that has the path to the legacy file stored as a hash for the filename.

Development

Run tests with just:

$ just test

Lint the codebase with:

$ just lint-fix