CLI stands for Command Line Interface.

It is a program that you can run from the terminal.
Ex: npm and git

Building a Custom CLI Tool

First, create a project folder under which create a package.json file by running the command:

bash
npm init --yes

Now, create an entry point file index.js with the hashbang:

js
#!/usr/bin/env node

console.log('Node JS Pokedex');

Now, add bin field in package.json:

json
...
  "bin": {
    "pokedex-cli": "index.js"
  },
...

Install the package as:

bash
npm install -g

Now, run the command specified in bin field to run the tool:

bash
> pokedex-cli
< Node JS Pokedex

CLI Options

We can add options to CLI tools by manipulating argv.

js
#!/usr/bin/env node

const yargs = require('yargs');
const { argv } = yargs(process.argv)

const printFiveMoves = async (pokemonName) => {
    const res = await fetch(
        `https://pokeapi.co/api/v2/pokemon/${pokemonName}`
    );
    const pokemon = await res.json();
    const moves = pokemon.moves.map(({move}) => move.name);
    console.log(moves.slice(0, 5));
};

printFiveMoves(argv.pokemon);

In terminal:

bash
> pokedex-cli --pokemon=mew
[ 'pound', 'mega-punch', 'pay-day', 'fire-punch', 'ice-punch' ]

Adding Interactivity in CLI Tools

We can use packages to add interactivity to our CLI tools like - inquirer package.

js
#!/usr/bin/env node

const inquirer = require('inquirer');

const printFiveMoves = async (pokemonName) => {
    const res = await fetch(
        `https://pokeapi.co/api/v2/pokemon/${pokemonName}`
    );
    const pokemon = await res.json();
    const moves = pokemon.moves.map(({move}) => move.name);
    console.log(moves.slice(0, 5));
};

const prompt = inquirer.createPromptModule()
prompt([{
    type: "input",
    name: "pokemon",
    message: "Enter a pokemon name to view its 5 moves"
}]).then((ans) => {
    const pokemon = ans.pokemon;
    printFiveMoves(pokemon);
})

In terminal:

bash
> pokedex-cli
? Enter a pokemon name to view its 5 moves mew
[ 'pound', 'mega-punch', 'pay-day', 'fire-punch', 'ice-punch' ]