Guide for building TypeScript CLIs with Bun. Use when creating command-line tools, adding subcommands to existing CLIs, or building developer tooling. Covers argument parsing, subcommand patterns, output formatting, and distribution.
Installation
Details
Usage
After installing, this skill will be available to your AI coding assistant.
Verify installation:
skills listSkill Instructions
name: cli-builder description: Guide for building TypeScript CLIs with Bun. Use when creating command-line tools, adding subcommands to existing CLIs, or building developer tooling. Covers argument parsing, subcommand patterns, output formatting, and distribution. tags:
- cli
- typescript
- bun
- tooling
CLI Builder
Build TypeScript command-line tools with Bun.
When to Build a CLI
CLIs are ideal for:
- Developer tools and automation
- Project-specific commands (
swarm,bd, etc.) - Scripts that need arguments/flags
- Tools that compose with shell pipelines
Quick Start
Minimal CLI
#!/usr/bin/env bun
// scripts/my-tool.ts
const args = process.argv.slice(2);
const command = args[0];
if (!command || command === "help") {
console.log(`
Usage: my-tool <command>
Commands:
hello Say hello
help Show this message
`);
process.exit(0);
}
if (command === "hello") {
console.log("Hello, world!");
}
Run with: bun scripts/my-tool.ts hello
With Argument Parsing
Use parseArgs from Node's util module (works in Bun):
#!/usr/bin/env bun
import { parseArgs } from "util";
const { values, positionals } = parseArgs({
args: process.argv.slice(2),
options: {
name: { type: "string", short: "n" },
verbose: { type: "boolean", short: "v", default: false },
help: { type: "boolean", short: "h", default: false },
},
allowPositionals: true,
});
if (values.help) {
console.log(`
Usage: greet [options] <message>
Options:
-n, --name <name> Name to greet
-v, --verbose Verbose output
-h, --help Show help
`);
process.exit(0);
}
const message = positionals[0] || "Hello";
const name = values.name || "World";
console.log(`${message}, ${name}!`);
if (values.verbose) {
console.log(` (greeted at ${new Date().toISOString()})`);
}
Subcommand Pattern
For CLIs with multiple commands, use a command registry:
#!/usr/bin/env bun
import { parseArgs } from "util";
type Command = {
description: string;
run: (args: string[]) => Promise<void>;
};
const commands: Record<string, Command> = {
init: {
description: "Initialize a new project",
run: async (args) => {
const { values } = parseArgs({
args,
options: {
template: { type: "string", short: "t", default: "default" },
},
});
console.log(`Initializing with template: ${values.template}`);
},
},
build: {
description: "Build the project",
run: async (args) => {
const { values } = parseArgs({
args,
options: {
watch: { type: "boolean", short: "w", default: false },
},
});
console.log(`Building...${values.watch ? " (watch mode)" : ""}`);
},
},
};
function showHelp() {
console.log(`
Usage: mytool <command> [options]
Commands:`);
for (const [name, cmd] of Object.entries(commands)) {
console.log(` ${name.padEnd(12)} ${cmd.description}`);
}
console.log(`
Run 'mytool <command> --help' for command-specific help.
`);
}
// Main
const [command, ...args] = process.argv.slice(2);
if (!command || command === "help" || command === "--help") {
showHelp();
process.exit(0);
}
const cmd = commands[command];
if (!cmd) {
console.error(`Unknown command: ${command}`);
showHelp();
process.exit(1);
}
await cmd.run(args);
Output Formatting
Colors (without dependencies)
const colors = {
reset: "\x1b[0m",
red: "\x1b[31m",
green: "\x1b[32m",
yellow: "\x1b[33m",
blue: "\x1b[34m",
dim: "\x1b[2m",
bold: "\x1b[1m",
};
function success(msg: string) {
console.log(`${colors.green}✓${colors.reset} ${msg}`);
}
function error(msg: string) {
console.error(`${colors.red}✗${colors.reset} ${msg}`);
}
function warn(msg: string) {
console.log(`${colors.yellow}⚠${colors.reset} ${msg}`);
}
function info(msg: string) {
console.log(`${colors.blue}ℹ${colors.reset} ${msg}`);
}
JSON Output Mode
Support --json for scriptable output:
const { values } = parseArgs({
args: process.argv.slice(2),
options: {
json: { type: "boolean", default: false },
},
allowPositionals: true,
});
const result = { status: "ok", items: ["a", "b", "c"] };
if (values.json) {
console.log(JSON.stringify(result, null, 2));
} else {
console.log("Status:", result.status);
console.log("Items:", result.items.join(", "));
}
Progress Indicators
function spinner(message: string) {
const frames = ["⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"];
let i = 0;
const id = setInterval(() => {
process.stdout.write(`\r${frames[i++ % frames.length]} ${message}`);
}, 80);
return {
stop: (finalMessage?: string) => {
clearInterval(id);
process.stdout.write(`\r${finalMessage || message}\n`);
},
};
}
// Usage
const spin = spinner("Loading...");
await someAsyncWork();
spin.stop("✓ Done!");
File System Operations
import { readFile, writeFile, mkdir, readdir } from "fs/promises";
import { existsSync } from "fs";
import { join, dirname } from "path";
// Ensure directory exists before writing
async function writeFileWithDir(path: string, content: string) {
await mkdir(dirname(path), { recursive: true });
await writeFile(path, content);
}
// Read JSON with defaults
async function readJsonFile<T>(path: string, defaults: T): Promise<T> {
if (!existsSync(path)) return defaults;
const content = await readFile(path, "utf-8");
return { ...defaults, ...JSON.parse(content) };
}
Shell Execution
import { $ } from "bun";
// Simple command
const result = await $`git status`.text();
// With error handling
try {
await $`npm test`.quiet();
console.log("Tests passed!");
} catch (error) {
console.error("Tests failed");
process.exit(1);
}
// Capture output
const branch = await $`git branch --show-current`.text();
console.log(`Current branch: ${branch.trim()}`);
Error Handling
class CLIError extends Error {
constructor(message: string, public exitCode = 1) {
super(message);
this.name = "CLIError";
}
}
async function main() {
try {
await runCommand();
} catch (error) {
if (error instanceof CLIError) {
console.error(`Error: ${error.message}`);
process.exit(error.exitCode);
}
throw error; // Re-throw unexpected errors
}
}
main();
Distribution
package.json bin field
{
"name": "my-cli",
"bin": {
"mycli": "./dist/cli.js"
},
"scripts": {
"build": "bun build ./src/cli.ts --outfile ./dist/cli.js --target node"
}
}
Shebang for direct execution
#!/usr/bin/env bun
// First line of your CLI script
Make executable: chmod +x scripts/my-cli.ts
Best Practices
- Always provide --help - Users expect it
- Exit codes matter - 0 for success, non-zero for errors
- Support --json - For scriptability and piping
- Fail fast - Validate inputs early
- Be quiet by default - Use --verbose for noise
- Respect NO_COLOR - Check
process.env.NO_COLOR - Stream large output - Don't buffer everything in memory
More by joelhooks
View allCI/CD publishing workflow for npm packages using Changesets + npm Trusted Publishers (OIDC). Use when setting up automated npm publishing for monorepos, configuring GitHub Actions for releases, troubleshooting workspace:* protocol resolution issues, fixing "Cannot find module" errors in published packages, or debugging npm OIDC authentication. Covers Bun + Turborepo + Changesets + npm Trusted Publishers with workspace protocol resolution.
GitHub issue triage workflow with contributor profile extraction. Analyze → clarify → file cells → tag → implement → credit. Captures Twitter handles for changeset acknowledgments.
Test-Driven Development workflow with RED-GREEN-REFACTOR, lore from Kent Beck, Michael Feathers, and Ousterhout's counterpoint
Context-efficient PR comment triage. Evaluate, decide, act. Fix important issues, resolve the rest silently.