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Using the Ruby Host SDK

Check your installation

Please be sure you've installed Extism before continuing with this guide.

1. Install the Ruby gem

The gem is hosted on RubyGems. Put the extism gem in your Gemfile:

gem "extism", "~> 0.5.0"

Or install with gem install if you are not using bundler:

gem install extism

2. Require the library and use the APIs

Count Vowels Plugin

code.wasm in this example is our example plugin that counts vowels. If you want to run this, download it first and set the path:

curl > code.wasm
require 'extism'
require 'json'

manifest = {
:wasm => [{:path => "code.wasm"}]

# NOTE: if you encounter an error such as:
# "Unable to load plugin: unknown import: wasi_snapshot_preview1::fd_write has not been defined"
# pass `true` after `manifest` in the following function to provide WASI imports to your plugin.
plugin =
res = JSON.parse("count_vowels", ARGV[0] || "this is a test"))

puts res['count']

Need help?

If you've encountered a bug or think something is missing, please open an issue on the Extism GitHub repository.

There is an active community on Discord where the project maintainers and users can help you. Come hang out!