Tab

Shell autocompletions are largely missing in the JavaScript CLI ecosystem. tab provides a simple API for adding autocompletions to any JavaScript CLI tool.

Additionally, tab supports autocompletions for pnpm, npm, yarn, and bun.

Modern CLI libraries like Gunshi include tab completion natively in their core.

As CLI tooling authors, if we can spare our users a second or two by not checking documentation or writing the -h flag, we’re doing them a huge favor. The unconscious mind loves hitting the [TAB] key and always expects feedback. When nothing happens, it breaks the user’s flow - a frustration apparent across the whole JavaScript CLI tooling ecosystem.

tab solves this complexity by providing autocompletions that work consistently across zsh, bash, fish, and powershell.

Installation

npm install @bomb.sh/tab
# or
pnpm add @bomb.sh/tab
# or
yarn add @bomb.sh/tab
# or
bun add @bomb.sh/tab

Quick Start

Add autocompletions to your CLI tool:

import t from '@bomb.sh/tab';

// Define your CLI structure
const devCmd = t.command('dev', 'Start development server');
devCmd.option('port', 'Specify port', (complete) => {
  complete('3000', 'Development port');
  complete('8080', 'Production port');
});

// Handle completion requests
if (process.argv[2] === 'complete') {
  const shell = process.argv[3];
  if (shell === '--') {
    const args = process.argv.slice(4);
    t.parse(args);
  } else {
    t.setup('my-cli', 'node my-cli.js', shell);
  }
}

Test your completions:

node my-cli.js complete -- dev --port=<TAB>
# Output: --port=3000  Development port
#         --port=8080  Production port

Install for users:

# One-time setup
source <(my-cli complete zsh)

# Permanent setup
my-cli complete zsh > ~/.my-cli-completion.zsh
echo 'source ~/.my-cli-completion.zsh' >> ~/.zshrc

Package Manager Completions

As mentioned earlier, tab provides completions for package managers as well:

# Generate and install completion scripts
npx @bomb.sh/tab pnpm zsh > ~/.pnpm-completion.zsh && echo 'source ~/.pnpm-completion.zsh' >> ~/.zshrc
npx @bomb.sh/tab npm bash > ~/.npm-completion.bash && echo 'source ~/.npm-completion.bash' >> ~/.bashrc
npx @bomb.sh/tab yarn fish > ~/.config/fish/completions/yarn.fish
npx @bomb.sh/tab bun powershell > ~/.bun-completion.ps1 && echo '. ~/.bun-completion.ps1' >> $PROFILE

Example in action:

pnpm install --reporter=<TAB>
# Shows: append-only, default, ndjson, silent

yarn add --emoji=<TAB>
# Shows: true, false

Framework Adapters

tab provides adapters for popular JavaScript CLI frameworks.

CAC Integration

import cac from 'cac';
import tab from '@bomb.sh/tab/cac';

const cli = cac('my-cli');

// Define your CLI
cli
  .command('dev', 'Start dev server')
  .option('--port <port>', 'Specify port')
  .option('--host <host>', 'Specify host');

// Initialize tab completions
const completion = await tab(cli);

// Add custom completions for option values
const devCommand = completion.commands.get('dev');
const portOption = devCommand?.options.get('port');
if (portOption) {
  portOption.handler = (complete) => {
    complete('3000', 'Development port');
    complete('8080', 'Production port');
  };
}

cli.parse();

Citty Integration

import { defineCommand, createMain } from 'citty';
import tab from '@bomb.sh/tab/citty';

const main = defineCommand({
  meta: { name: 'my-cli', description: 'My CLI tool' },
  subCommands: {
    dev: defineCommand({
      meta: { name: 'dev', description: 'Start dev server' },
      args: {
        port: { type: 'string', description: 'Specify port' },
        host: { type: 'string', description: 'Specify host' },
      },
    }),
  },
});

// Initialize tab completions
const completion = await tab(main);

// Add custom completions
const devCommand = completion.commands.get('dev');
const portOption = devCommand?.options.get('port');
if (portOption) {
  portOption.handler = (complete) => {
    complete('3000', 'Development port');
    complete('8080', 'Production port');
  };
}

const cli = createMain(main);
cli();

Commander.js Integration

import { Command } from 'commander';
import tab from '@bomb.sh/tab/commander';

const program = new Command('my-cli');
program.version('1.0.0');

// Define commands
program
  .command('serve')
  .description('Start the server')
  .option('-p, --port <number>', 'port to use', '3000')
  .option('-H, --host <host>', 'host to use', 'localhost')
  .action((options) => {
    console.log('Starting server...');
  });

// Initialize tab completions
const completion = tab(program);

// Add custom completions
const serveCommand = completion.commands.get('serve');
const portOption = serveCommand?.options.get('port');
if (portOption) {
  portOption.handler = (complete) => {
    complete('3000', 'Default port');
    complete('8080', 'Alternative port');
  };
}

program.parse();

How It Works

tab uses a standardized completion protocol that any CLI can implement:

# Generate shell completion script
my-cli complete zsh

# Parse completion request (called by shell)
my-cli complete -- install --port=""

Output Format:

--port=3000    Development port
--port=8080    Production port
:4

Contributing

We welcome contributions! tab’s architecture makes it easy to add support for new package managers or CLI frameworks.

Acknowledgments

tab was inspired by the great Cobra project, which set the standard for CLI tooling in the Go ecosystem.

Adoption Support

We want to make it as easy as possible for the JS ecosystem to enjoy great autocompletions.
We at Thundraa would be happy to help any open source CLI utility adopt tab. If you maintain a CLI and would like autocompletions set up for your users, just drop the details in our Adopting tab discussion.
We’ll gladly help and even open a PR to get you started.