1. Built-in defaults (hardcoded)
2. System config   (/etc/<tool>/config)
3. User config     (~/.config/<tool>/config or ~/.<tool>rc)
4. Project config  (./<tool>.config.json or ./<tool>rc)
5. Environment vars (TOOL_OPTION=value)
6. CLI flags       (--option value)

import { Command } from 'commander';

const program = new Command();

program
  .name('mytool')
  .description('A CLI that does useful things')
  .version('1.0.0');

program
  .command('deploy')
  .description('Deploy the application to a target environment')
  .argument('<environment>', 'target environment (staging, production)')
  .option('-d, --dry-run', 'show what would happen without deploying')
  .option('-t, --tag <tag>', 'docker image tag to deploy', 'latest')
  .option('--timeout <ms>', 'deploy timeout in milliseconds', '30000')
  .action((environment, options) => {
    if (options.dryRun) {
      console.log(`Would deploy ${options.tag} to ${environment}`);
      return;
    }
    deploy(environment, options.tag, parseInt(options.timeout, 10));
  });

program.parse();

import click

@click.group()
@click.version_option("1.0.0")
def cli():
    """A CLI that does useful things."""
    pass

@cli.command()
@click.argument("environment", type=click.Choice(["staging", "production"]))
@click.option("--dry-run", "-d", is_flag=True, help="Show what would happen.")
@click.option("--tag", "-t", default="latest", help="Docker image tag.")
@click.option("--timeout", default=30000, type=int, help="Timeout in ms.")
def deploy(environment, dry_run, tag, timeout):
    """Deploy the application to a target environment."""
    if dry_run:
        click.echo(f"Would deploy {tag} to {environment}")
        return
    do_deploy(environment, tag, timeout)

if __name__ == "__main__":
    cli()

import { confirm, select, input } from '@inquirer/prompts';

async function interactiveSetup() {
  const name = await input({
    message: 'Project name:',
    default: 'my-project',
    validate: (v) => v.length > 0 || 'Name is required',
  });

  const template = await select({
    message: 'Choose a template:',
    choices: [
      { name: 'Minimal', value: 'minimal' },
      { name: 'Full-stack', value: 'fullstack' },
      { name: 'API only', value: 'api' },
    ],
  });

  const proceed = await confirm({
    message: `Create "${name}" with ${template} template?`,
    default: true,
  });

  if (!proceed) {
    console.log('Aborted.');
    process.exit(0);
  }
  return { name, template };
}

import { cosmiconfig } from 'cosmiconfig';

const explorer = cosmiconfig('mytool', {
  searchPlaces: [
    'package.json',
    '.mytoolrc',
    '.mytoolrc.json',
    '.mytoolrc.yaml',
    'mytool.config.js',
    'mytool.config.ts',
  ],
});

async function loadConfig(flagOverrides: Record<string, unknown>) {
  const result = await explorer.search();
  const fileConfig = result?.config ?? {};

  // Merge: defaults < file config < env vars < flags
  return {
    output: 'dist',
    verbose: false,
    ...fileConfig,
    ...(process.env.MYTOOL_OUTPUT ? { output: process.env.MYTOOL_OUTPUT } : {}),
    ...flagOverrides,
  };
}

Usage: mytool deploy [options] <environment>

Deploy the application to a target environment.

Arguments:
  environment          target environment (staging, production)

Options:
  -d, --dry-run        show what would happen without deploying
  -t, --tag <tag>      docker image tag to deploy (default: "latest")
      --timeout <ms>   deploy timeout in milliseconds (default: "30000")
  -h, --help           display help for command

Examples:
  $ mytool deploy staging
  $ mytool deploy production --tag v2.1.0 --dry-run

import { createReadStream } from 'fs';
import { stdin as processStdin } from 'process';

function getInputStream(filePath?: string): NodeJS.ReadableStream {
  if (filePath) return createReadStream(filePath);
  if (!process.stdin.isTTY) return processStdin;
  console.error('Error: No input. Provide a file or pipe stdin.');
  console.error('  mytool process <file>');
  console.error('  cat file.txt | mytool process');
  process.exit(2);
}

function output(data: unknown, json: boolean) {
  if (json) {
    process.stdout.write(JSON.stringify(data) + '\n');
  } else {
    console.log(formatHuman(data));
  }
}

{
  "name": "mytool",
  "bin": { "mytool": "./dist/cli.js" },
  "files": ["dist"],
  "engines": { "node": ">=18" }
}

[project.scripts]
mytool = "mytool.cli:cli"

undefined

```rust
// Clap: generate completions via clap_complete
use clap_complete::{generate, shells::Zsh};
generate(Zsh, &mut cli, "mytool", &mut std::io::stdout());