Develop a ulauncher extension with a command database

Over the weekend, I picked up a project via Reddit involving a plugin for the Flow Launcher. I created a fzf and rofi version for my Ubuntu Linux environment, and then thought, how hard can it be to port it to uLauncher?

Here I document what I did.

1. Inside ~/.local/share/ulauncher/extensions/

create a new dir. In my case, I created ~/.local/share/ulauncher/extensions/com.github.ubuntupunk.ulauncher-vim

2. Touch the following files:

├── images
│   └── icon.png
├── versions.json
├── manifest.json
└── main.py

3. In versions.json place the following boilerplate:

[
  {"required_api_version": "2", "commit": "master"}
]

4. In manifest.json

{
  "required_api_version": "2",
  "name": "Demo extension",
  "description": "Extension Description",
  "developer_name": "John Doe",
  "icon": "images/icon.png",
  "options": {
    "query_debounce": 0.1
  },
  "preferences": [
    {
      "id": "demo_kw",
      "type": "keyword",
      "name": "Demo",
      "description": "Demo extension",
      "default_value": "dm"
    }
  ]
}

5. In main.py

from ulauncher.api.client.Extension import Extension
from ulauncher.api.client.EventListener import EventListener
from ulauncher.api.shared.event import KeywordQueryEvent, ItemEnterEvent
from ulauncher.api.shared.item.ExtensionResultItem import ExtensionResultItem
from ulauncher.api.shared.action.RenderResultListAction import RenderResultListAction
from ulauncher.api.shared.action.HideWindowAction import HideWindowAction


class DemoExtension(Extension):

    def __init__(self):
        super().__init__()
        self.subscribe(KeywordQueryEvent, KeywordQueryEventListener())


class KeywordQueryEventListener(EventListener):

    def on_event(self, event, extension):
        items = []
        for i in range(5):
            items.append(ExtensionResultItem(icon='images/icon.png',
                                             name='Item %s' % i,
                                             description='Item description %s' % i,
                                             on_enter=HideWindowAction()))

        return RenderResultListAction(items)

if __name__ == '__main__':
    DemoExtension().run()

6. Now edit manifest.json

{
  "required_api_version": "2",
  "name": "Vim Prompter",
  "description": "Vim cheatsheet helper",
  "developer_name": "David Robert Lewis",
  "icon": "images/icon.png",
  "options": {
    "query_debounce": 0.1
  },
  "preferences": [
    {
      "id": "vm_kw",
      "type": "keyword",
      "name": "Vim",
      "description": "Search for Vim commands",
      "default_value": "vm"
    }
  ]

7. Add command loading function to main.py

class VmExtension(Extension):
    def load_vim_commands(self):
        """Load Vim commands from JSON file."""
        package_dir = os.path.dirname(os.path.abspath(__file__))
        full_path = os.path.join(package_dir, 'db', 'commands.json')   
        with open(full_path, 'r') as file:
            return json.load(file)

    def __init__(self):
        super().__init__()
        self.vim_commands = self.load_vim_commands()
        self.subscribe(KeywordQueryEvent, KeywordQueryEventListener())

8. Create a db folder with the following:

commands.json

example structure:

{
  "categories": {
    "navigation": {
      "name": "Navigation",
      "patterns": [
        "scroll",
        "jump",
        "goto",
        "position"
      ],
      "subcategories": {
        "cursor": {
          "name": "Cursor Movement",
          "patterns": [
            "move[s]? cursor",
            "^[hjkl]$",
            "^[HJKL]$",
            "^[wWeEbB]$"
          ]
        },

You can see the entire commands.json here.

9. Modify the KeywordQueryEventListener to implement the search functionality.

class KeywordQueryEventListener(EventListener):
    def on_event(self, event, extension):
        query = event.get_argument() or ""
        items = []

        # If no query, show all commands (limited to first 8)
        commands_to_show = extension.vim_commands

        # If there's a query, filter commands
        if query:
            commands_to_show = [
                cmd for cmd in extension.vim_commands
                if query.lower() in cmd['command'].lower() or 
                   query.lower() in cmd['description'].lower()
            ]

        # Limit results to first 8 matches
        for cmd in commands_to_show[:8]:
            items.append(ExtensionResultItem(
                icon='images/icon.png',
                name=cmd['command'],
                description=f"{cmd['name']} - {cmd['description']}",
                on_enter=HideWindowAction()
            ))

        return RenderResultListAction(items)

10. Add the URL opening functionality. We'll need to import webbrowser and modify the on_enter action to open the Vim command URL

from ulauncher.api.shared.action.OpenUrlAction import OpenUrlAction

class KeywordQueryEventListener(EventListener):
    def on_event(self, event, extension):
        query = event.get_argument() or ""
        items = []

        commands_to_show = extension.vim_commands

        if query:
            commands_to_show = [
                cmd for cmd in extension.vim_commands
                if query.lower() in cmd['command'].lower() or 
                   query.lower() in cmd['description'].lower()
            ]

        for cmd in commands_to_show[:8]:
            url = f"https://vim.rtorr.com/#:~:text={cmd['rtorr_description']}"
            items.append(ExtensionResultItem(
                icon='images/icon.png',
                name=cmd['command'],
                description=f"{cmd['name']} - {cmd['description']}",
                on_enter=OpenUrlAction(url)
            ))

        return RenderResultListAction(items)

11. Key changes are:

• Added OpenUrlAction import
• Replaced HideWindowAction with OpenUrlAction
• Constructed the URL using the command's rtorr_description

12. The full project code can be viewed here:

ulauncher-vim repo

and the ulauncher extension here

References

1. https://dev.to/brpaz/an-introduction-to-ulauncher-extension-development-1m69
2. https://ext.ulauncher.io/-/github-ubuntupunk-ulauncher-vim

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