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Version: 4.0.0

Tutorial: Build a CLI Plugin

Build a helm system-info command that displays system information.

Subprocess Runtime​

Let's start by building a CLI Plugin with the Subprocess runtime.

Prerequisites​

  1. Install the latest Helm 4 release: v4.0.0
  2. In your terminal session, alias helm to the release you downloaded. helm version --short should now show the correct Helm version in this terminal session.

1. Create Plugin Directory​

You can create this anywhere on your filesystem. For example:

mkdir -p $HOME/code/helm/plugins/system-info
cd $HOME/code/helm/plugins/system-info

2. Create plugin manifest​

plugin.yaml
apiVersion: v1
type: cli/v1
name: "system-info"
version: "0.1.0"
runtime: subprocess
config:
  usage: system-info
  shortHelp: Display system and Helm information
  longHelp: Shows OS info, Helm version, and environment details
runtimeConfig:
  platformCommand:
    - command: ${HELM_PLUGIN_DIR}/system-info.sh

3. Create Script​

system-info.sh
#!/bin/bash

echo "=== System Information ==="
echo "OS: $(uname -s)"
echo "Architecture: $(uname -m)"

echo ""
echo "=== Helm Information ==="
echo "Plugin Dir: $HELM_PLUGIN_DIR"
echo "Arguments: $*"

echo ""
echo "System info complete!"

Make it executable:

chmod +x system-info.sh

4. Install in Dev Mode and Test​

Installing a plugin from your filesystem installs in local dev mode. This bypasses checking or verifying provenance:

% helm plugin install $HOME/code/helm/plugins/system-info
Installing plugin from local directory (development mode)
Installed plugin: system-info

Local dev mode installation creates a symlink from your source directory to the plugins directory, so you can continue to develop in your preferred location. You can see the symlink by listing the directory location using the internal HELM_PLUGINS env variable:

% ls -lah $(helm env HELM_PLUGINS)
total 0
drwxr-xr-x@ 3 r6by  staff    96B Nov 10 02:18 .
drwxr-xr-x@ 3 r6by  staff    96B Jan 21  2025 ..
lrwxr-xr-x  1 r6by  staff    41B Nov 10 02:18 system-info -> /Users/r6by/code/helm/plugins/system-info

You can see your plugin details in the helm plugin list of installed plugins:

% helm plugin list
NAME       	VERSION	TYPE  	APIVERSION	PROVENANCE	SOURCE
system-info	0.1.0  	cli/v1	v1        	local dev 	unknown

You can also now see your plugin in the list of available commands with helm help, and see it's own generated help message you defined in your plugin.yaml:

% helm help | grep system-info
  system-info Display system and Helm information

% helm help system-info
Shows OS info, Helm version, and environment details

Usage:
  helm system-info [flags]

Let's try running the CLI subcommand:

% helm system-info
=== System Information ===
OS: Darwin
Architecture: arm64

=== Helm Information ===
Plugin Dir: /Users/r6by/Library/helm/plugins/system-info
Arguments:

System info complete!

What you built: A CLI plugin using the Subprocess runtime!

Now let's do it again, this time using Wasm runtime…

Wasm Runtime​

Prerequisites​

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To-do: add this section