asdf is a great tool for managing multiple versions of command-line tools. 99% of the time these managed tools work just as expected.

Shims are just tiny wrappers created by asdf that just forward execution to the real versioned executables installed by asdf. This way, asdf has a single shims directory added to your PATH and has no need of mangling the PATH for every installed version.

When you run an asdf-managed command, like node, it will actually execute an asdf-shim, which will determine the node version to activate according to your .tool-versions file.

A downside of this is that every single time you run node asdf will have to determine again which version to use. Even if you haven't changed your .tool-versions file to upgrade the node version to use. And this happens for every shim execution, which could lead to some users experiencing certain slowness while asdf is looking up versions, since it has to traverse directories looking up for a .tool-versions file and probably also legacy version files.

Another inconvenience is that commands installed by these tools can have some problems by the way asdf shims work. For example, if a command tries to find itself by name in PATH (e.g. using which my-command) it will find the asdf shim executable and not the actual executable delegated-to by asdf. This might cause problems if the command tries to use this location as an installation root to find auxiliary files, since shims will mask the real executable.

Also, people frequently ask why is reshim needed. Suppose you used asdf to install a package manager like npm, hex, gem, cargo, etc. Any new binaries installed by these tools won't be available on PATH unless you run asdf reshim. This is because asdf has no way of knowing what the npm install command does, and it's until asdf reshim that it will figure out new executables are available and will create shims for them accordingly.

And finally, some packages come not only with language-specific commands, but with tons of system tools that will shadow those already installed on your system. While this may be desirable while the language is in use, having it installed and not activated leaves dead shims all over the place.

All these previously mentioned issues can be solved by using asdf along with the direnv tool.

Just like asdf is a tools manager, direnv is an environment-variables manager. It can update your shell env upon directory change and clean it up when you leave that directory.

This asdf-direnv plugin lets you install direnv and also provides a tiny script to integrate both. Allowing direnv to manage any variables exposed by asdf tools, primarily the PATH environment, but also any other variable exposed by your plugin (e.g. MIX_HOME exposed by the asdf-elixir plugin).

This way, running node will not invoke the asdf-shim but the real asdf-managed executable in PATH. Which will improve speed since version resolution is out of the way and made only once by direnv upon entering your project directory. Commands trying to find themselves in PATH will find their expected location. Also, no more reshim needed upon npm install.

Updating this plugin is the same as any asdf plugin:

asdf plugin update direnv

Updating the version of direnv you use depends on which installation method you've chosen:

• system: Nothing special required here, whenever your system package manager updates direnv, this plugin will use the updated version.

• latest or <direnv-release-version>: Re-run asdf direnv setup --version latest --shell ... to update to the latest version of direnv.

To speed up things a lot, this plugin creates direnv envrc files that contain your tools environment. They are created automatically whenever your .envrc or your .tool-versions files change.

Cached environment files can be found under $XDG_CACHE_HOME/asdf-direnv/env. On most systems that resolves to ~/.config/asdf-direnv/env. It's always safe to remove files on this directory since they will be re-generated if missing.

If you ever need to regenerate a cached environment file, just touch .envrc.

Also, the asdf direnv envrc command will print the path to the cached environment file used for your project.

Now when you leave your project directory and come back to it, direnv will manage the environment variables for you really fast. For example:

direnv: loading .envrc
direnv: using asdf
direnv: Creating env file ~/.cache/asdf-direnv/env/909519368-2773408541-1591703797-361987458
direnv: loading ~/.cache/asdf-direnv/env/909519368-2773408541-1591703797-361987458
direnv: using asdf elixir 1.8.1-otp-21
direnv: using asdf nodejs 12.6.0
direnv: export +MIX_ARCHIVES +MIX_HOME +NPM_CONFIG_PREFIX ~PATH

node --version

with asdf-direnv:

without asdf-direnv:

hyperfine 'node --version'

npm install -g yarn

with asdf-direnv:

without asdf-direnv:

hyperfine --cleanup 'npm uninstall -g yarn' 'npm install -g yarn'

• Take a look at direnv help true.

• Getting $ASDF_DIR/shims out of the PATH.

  Some users might want to bypass asdf shims altogether. To do so, include only $ASDF_DIR/bin in your PATH but exclude the shims directory.

  All shims are still available via asdf exec <shim>

# ~/.bashrc or equivalent

# Don't source `~/.asdf/asdf.sh`
PATH="$PATH:~/.asdf/bin"

• If you want to silence the console output of direnv, you can do that by setting an empty environment variable: export DIRENV_LOG_FORMAT="".

• Some times you might need to configure IDEs or other tools to find executables like package managers/code linters/compilers being used on a project of yours. For example, to execute npm outside your project directory you can do:

direnv exec /some/project npm

• Remember that activation order is important.

  If a local .tool-versions file is present, the order of listed plugins will be preserved, so that toolA will be present before toolB in PATH.

# .tool-versions
toolA 1.0
toolB 2.0

• You can use asdf even if current directory has no .tool-versions file.

  In this case the the activated versions will be the same than those returned by asdf current command.

• You can override any tool version via environment variables.

  See the asdf documentation regarding versions from environment variables.

# .envrc
export ASDF_PLUGIN_VERSION=1.0
use asdf

• Remember direnv can reload the environment whenever a file changes. By default this plugin will watch any .tool-versions file or legacy version file that explicitly selects a tool.

But you can easily watch more files when needed.

# .envrc
watch_file "package.json"

• Using direnv status can be helpful to inspect current state. Also, you might want to take a look to direnv --help.

• Using a non-empty ASDF_DIRENV_DEBUG will enable bash-tracing with set -x and skip env-cache.

  For example, if you are troubleshooting or trying to debug something weird on your environment, use env ASDF_DIRENV_DEBUG=true direnv reload and provide any relevant output on an issue.

  Also, if you are contributing a new feature or bug-fix try running env ASDF_DIRENV_DEBUG=true bats -x test to run all tests with trace mode. If any test fails you will see more output.