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Extism CLI

The extism CLI is a useful but optional tool for developing on Extism. It handles a few things such as installing the shared library (Extism Runtime), or invoking plug-ins from the command line.

The following instructions will walk you through how to install the Extism CLI, and then the installation of the shared library which a Host SDK will look for automatically.

Install the Extism CLI

curl -s | sh

Or to a specific path:

curl -s | sh -s -- -o $HOME/.local/bin

See the help output for more information:

curl -s | sh -s -- -h

Releases are also available on Github:

Remove old installation

If you have installed the old cli via python, you may need to remove it:

pip3 uninstall extism_cli --break-system-packages
which extism # shouldn't print anything, if it does, delete it

Using the Extism CLI

The most common use-case is to to install Extism from Github releases, and then install the library and header file into the installation prefix of your choice. The default prefix is /usr/local, so libraries will be installed to /usr/local/lib and the header will be installed to /usr/local/include.


Some language SDKs come bundled with the runtime and some need you to install the runtime separately. If your language needs you to install the runtime, the SDKs readme will say so in the install instructions.

sudo extism lib install

sudo may use a different path than your user. If so, you may need to tell sudo to use the PATH defined for your user with: sudo -E env "PATH=$PATH" extism lib install

Installing the latest from git

It's also possible to install the latest build from the main git branch:

sudo extism lib install --version git

Overriding install location

Pass the --prefix argument a path on disk where extism CLI will install the system files:

extism lib install --prefix ~/.local

Other CLI Features

extism [command]

Available Commands:
call Call a plugin function
completion Generate the autocompletion script for the specified shell
help Help about any command
lib Manage libextism

--github-token string Github access token, can also be set using the $GITHUB_TOKEN env variable
-h, --help help for extism
-q, --quiet Enable additional logging
-v, --verbose Enable additional logging
--version version for extism

Use "extism [command] --help" for more information about a command.

Call plug-in functions

You can use the extism CLI as a test runner to check your plug-ins outside of any Host program:

extism call --input "this is a test" test/code.wasm count_vowels
{"count": 4}

Check installed version

The CLI can also be used to get information about the installed version of libextism:

extism lib check