Shims

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The beginner's guide, and my blog post are helpful resources to dive deeper into shims.

Introduction

There are two ways for dev tools to be loaded into your shell: mise activate and shims.

• Mise's "PATH" activation method updates environment variables at each prompt by modifying PATH
• The "shims" method uses symlinks to the mise binary that intercept commands and load the appropriate environment

While the PATH design of mise works great in most cases, there are some situations where shims are preferable. One example is when calling mise binaries from an IDE.

To support this, mise does have a shim dir that can be used. It's located at ~/.local/share/mise/shims.

$ mise use -g node@20
$ npm install -g [email protected]
$ mise reshim # may be required if new shims need to be created after installing packages
$ ~/.local/share/mise/shims/node -v
v20.0.0
$ ~/.local/share/mise/shims/prettier -v
3.1.0

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mise activate --shims is a shorthand for adding the shims directory to PATH.

INFO

mise reshim actually should get called automatically if you're using npm so an explicit reshim should not be necessary in that scenario. Also, this bears repeating but: mise reshim just creates/removes the shims. People use it as a "fix it" button but it really should only be necessary if ~/.local/share/mise/shims doesn't contain something it should.

mise also runs a reshim anytime a tool is installed/updated/removed so you don't need to use it for those scenarios.

Also don't put things in there manually, mise will just delete it next reshim.

How to add mise shims to PATH

If you prefer to use shims, you can run the following to use mise without activating it.

You can use .bashrc/.zshrc instead of .bash_profile/.zprofile if you prefer to only use mise in interactive sessions (.bash_profile/.zprofile will work in non-interactive places like scripts or IDEs). Note that mise activate will remove the shims directory so it's fine to call mise activate --shims in the profile file then later call mise activate in an interactive session.

bash

# note that bash will read from ~/.profile or ~/.bash_profile if the latter exists
# ergo, you may want to check to see which is defined on your system and only append to the existing file
echo 'eval "$(mise activate bash --shims)"' >> ~/.bash_profile # this sets up non-interactive sessions
echo 'eval "$(mise activate bash)"' >> ~/.bashrc       # this sets up interactive sessions

zsh

echo 'eval "$(mise activate zsh --shims)"' >> ~/.zprofile # this sets up non-interactive sessions
echo 'eval "$(mise activate zsh)"' >> ~/.zshrc    # this sets up interactive sessions

fish

echo 'mise activate fish --shims | source' >> ~/.config/fish/config.fish
echo 'mise activate fish | source' >> ~/.config/fish/fish.config

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You can also run export PATH="$HOME/.local/share/mise/shims:$PATH" which is what mise activate --shims does. This can be helpful is mise may not be available at that point in time. It's also a tiny bit faster, but since this is only run once per shell session it's not a big deal.

Shims vs PATH

In general, I recommend using PATH (mise activate) instead of shims for interactive situations. The way activate works is every time the prompt is displayed, mise-en-place will determine what PATH and other env vars should be and export them. This is why it doesn't work well for non-interactive situations like scripts. The prompt never gets displayed so you have to manually call mise hook-env to get mise to update the env vars.

Also, if you run a set of commands in a single line like the following:

cd ~
cd ~/src/proj1 && node -v && cd ~/src/proj2 && node -v

Using mise activate, this will use the tools from ~, not from ~/src/proj1 or ~/src/proj2 even after the directory changed because the prompt never got displayed. That might be obvious to you, not sure, what I'm trying to convey though is just think of mise running just before your prompt gets displayed—because that literally is what is happening. It's not a magical utility that is capable of having your environment always setup perfectly in every situation even though it might normally "feel" that way.

Note that shims will work with the inline example above.

INFO

This may be fixable at least for some shells if they support a hook for directory change, however some investigation will need to be done. See #1294 for details.

which

which is a command that I personally find great value in. shims effectively "break" which and cause it to show the location of the shim. Of course mise which will show the location but I prefer the "cleanliness" of running which node and getting back a real path with a version number inside of it. e.g:

$ which node
/Users/jdx/.mise/installs/node/20/bin/node

Env vars and shims

A downside of shims is the "mise environment" is only loaded when a shim is called. This means if you set an environment variable in mise.toml, it will only be run when a shim is called. So the following only works under mise activate:

$ mise set NODE_ENV=production
$ echo $NODE_ENV
production

But this will work in either:

$ mise set NODE_ENV=production
$ node -p process.env.NODE_ENV
production

Also, mise x|exec and mise r|run can be used to get the environment even if you don't need any mise tools:

$ mise set NODE_ENV=production
$ mise x -- bash -c "echo \$NODE_ENV"
production
$ mise r some_task_that_uses_NODE_ENV
production

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In general, tasks are a good way to ensure that the mise environment is always loaded so this isn't a problem.

Hook on cd

Some version managers modify the behavior of cd. That might seem like the ideal method of making a version manager, it has tons of gaps. It doesn't work if you use pushd|popd or other commands that modify PWD—though some shells have a "chpwd" hook that would. It doesn't run if you modify the mise.toml file.

The upside is that it doesn't run as frequently but since mise is written in rust the cost for executing mise is negligible (~4-5ms).

.zshrc/.bashrc files

rc files like .zshrc are unusual. It's a script but also runs only for interactive sessions. If you need to access tools provided by mise inside of an rc file you have 2 options:

hook-env

eval "$(mise activate zsh)"
eval "$(mise hook-env -s zsh)"
node some_script.js

shims

eval "$(mise activate zsh --shims)" # should be first
eval "$(mise activate zsh)"
node some_script.js

The only difference I can think of between these would be that using hook-env you will need to call it again if you change directories but with shims that won't be necessary. The shims directory will be removed by mise activate automatically so you won't need to worry about dealing with shims in your PATH.

Performance

Truthfully, you're probably not going to notice much in the way of performance with any solution here. However, I would like to document what the tradeoffs are since it's not as simple as "shims are slow". In asdf they are, but that's because asdf is written in bash. In mise the cost of the shims are negligible.

First, since mise runs every time the prompt is displayed with mise activate, you'll pay a few ms cost every time the prompt is displayed. Regardless of whether or not you're actively using a mise tool, you'll pay that penalty every time you run any command. It does have some short-circuiting logic to make it faster if there are no changes but it doesn't help much unless you have a very complex setup.

shims have basically the same performance profile but run when the shim is called. This makes some situations better, and some worse.

If you are calling a shim from within a bash script like this:

for i in {1..500}; do
    node script.js
done

You'll pay the mise penalty every time you call it within the loop. However, if you did the same thing but call a subprocess from within a shim (say, node creating a node subprocess), you will not pay a new penalty. This is because when a shim is called, mise sets up the environment with PATH for all tools and those PATH entries will be before the shim directory.

In other words, which is better in terms of performance just depends on how you're calling mise. Really though I think most users won't notice a 5ms lag on their terminal so I suggest mise activate.

Neither shims nor PATH

I don't actually use either of these methods. There are many ways to load the mise environment that don't require either, chiefly: mise x|exec and mise r|run.

These will both load all of the tools and env vars before executing something. I find this to be ideal because I don't need to modify my shell rc file at all and my environment is always loaded explicitly. I find this a "clean" way of working.

The obvious downside is that anytime I want to use mise I need to prefix it with mise exec|run, though I alias them to mx|mr.

This is what I'd recommend if you're like me and prefer things to be precise over "easy". Or perhaps if you're just wanting to use mise on a single project because that's what your team uses and prefer not to use it to manage anything else on your system. IMO using a shell extension for that use-case would be overkill.

Part of the reason for this is I often need to make sure I'm on my development version of mise. If you work on mise yourself I would recommend working in a similar way and disabling mise activate or shims while you are working on it.