_If a plugin supports downloading & compiling from source, you can specify `ref:foo` where `foo` is a specific branch, tag, or commit. You'll need to use the same name and reference when uninstalling too._
When asdf installs a package it creates shims for every executable program in that package in a `$ASDF_DATA_DIR/shims` directory (default `~/.asdf/shims`). This directory being on the `$PATH` (by means of `asdf.sh` or `asdf.fish`) is how the installed programs are made available in the environment.
The shims themselves are really simple wrappers that `exec` a helper program `asdf exec` passing it the name of the plugin and path to the executable in the installed package that the shim is wrapping.
The `asdf exec` helper determines the version of the package to use (as specified in `.tool-versions` file, selected by `asdf local ...` or `asdf global ...`), the final path to the executable in the package installation directory (this can be manipulated by the `exec-path` callback in the plugin) and the environment to execute in (also provided by the plugin - `exec-env` script), and finally it executes it.
!> Note that because this system uses `exec` calls, any scripts in the package that are meant to be sourced by the shell instead of executed need to be accessed directly instead of via the shim wrapper. The two asdf commands: `which` and `where` can help with this by returning the path to the installed package:
If for some reason you want to by-pass asdf shims or want your environment variables automatically set upon entering your project's directory, the [asdf-direnv](https://github.com/asdf-community/asdf-direnv) plugin can be helpful. Be sure to check its README for more details.