If you are a developer, you should be some how or familiar with command-line user interface(cli) because a lot of tools provide CLI such git, npm-cli, python-cli, dotnet-cli, aws-cli and more. CLI tools have many advantages than GUI tools like launch easily, development easily and cross-platform easily. Cli tool is good for you at some scenarios, for example, csv files import, batch jobs or schedule jobs. Therefore, this blog-post will show you a easy way to build a cross-platform CLI tool.

I use Nodejs to build the CLI tool. There are 3 benefits:

• Nodejs is cross-platform, CLI tools can be run on Windows, Mac and Linux.
• Easy to distribution. You can publish the cli tool to NPM or just make a package to install privately.
• Easy to build. Only few lines, the project can be turned to a CLI tool.

Requirement

• Nodejs

Try this command to see your computer has nodejs installed.

node --version

You can go to Nodejs to install it if you haven’t installed on your computer.

Hello World

Let’s start an easiest example.

Initialization

mkdir build-cli-example
cd build-cli-example
npm init --yes

Those commands will create a package.json.

Add bin in ./package.json

{
  "name": "build-cli-example",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "bin":{
    "my-cli" : "./my-cli"
  }
}

bin is the command name and we named it my-cli. Its value is a file like below.

Add ./my-cli file

#!/usr/bin/env node
require("./index.js")

The first line tells NPM what kind of environment the file is. It is very important because without this line. NPM cannot generate bin files correctly. The other lines are regular Nodejs code. There just calls ./index.js.

Add ./index.js file

console.log("hello would")

For our first step, we just print the greeting word.

Pack, Install and Test

npm pack
npm install -g build-cli-example-1.0.0.tgz
my-cli

The Execution Result

when you run npm install -g build-cli-example-1.0.0.tgz to install the package, npm will generate my-cli (sh file) and my-cli.cmd in the npm file. Because the npm file is in PATH, so when we type my-cli. The OS can find my-cli to execute.

Parameter Parser

The really CLI tool usually can allow users input some parameters to change its behaviors. You can use process.argv to get input parameters and parse them, but don’t build your own wheels if there are many parsers you can use. I recommend command-line-args, it is a very good parameter parser.

Install command-line-args

npm install --save command-line-args 

New ./index.js

const commandLineArgs = require('command-line-args')

const optionDefinitions = [
    { name: 'env', alias: "e", type: String, defaultValue: "local" },    
    { name: 'files', alias: "t", type: String, multiple: true },    
    { name: 'help', alias: "h", type: Boolean },
    { name: 'new', alias: "n", type: Boolean },
    { name: 'size', alias: "s", type: Number, defaultValue: 100 }
]

const options = commandLineArgs(optionDefinitions, { partial: true });

if (options.help || options._unknown) {
    if (options._unknown) {
        console.log("Unknown options:", options._unknown);
    }

    // TODO:Print Help
} else {
    // Do some jobs
}

The command-line-args is straight forward to use, you can see command-line-args for complete information.

Test

my-cli -e qa --files ./a.txt ./b.txt

Print Help

One thing I complain command-line-args is that its usage generation is separated to another package command-line-usage. So you have to define parser and usage on the different place.

Install command-line-usage

npm install -S command-line-usage

Replace TODO

const usage = require('command-line-usage');

const sections = [
    {
        header: 'My CLI',
        content: 'description'
    },
    {
        header: 'Options',
        optionList: [
            {
                name: 'new',
                alias: "n"
            },
            {
                name: 'size',
                alias: "s",
                description: 'Batch Size, default is 100'
            },
            {
                name: 'files',
                alias: "f",
                multiple: true,
                typeLabel: '[underline]{file} ...'
            },
            {
                name: 'env',
                alias: "e",
                description: 'Environment, default is local'
            },
            {
                name: 'help',
                alias: "h",
                description: 'Print the usage guide'
            }
        ]
    },
    {
        header: 'Examples',
        content: [
            {
                desc: "env",
                example: "my-cli --env dev"
            },
            {
                desc: "files",
                example: "my-cli --files a.txt b.txt"
            }
        ]
    },
]

console.log(usage(sections))

you can see command-line-args for complete information.

Test

Run npm pack and npm install -g as below to reinstall the package.

my-cli --help

Summary

This is the Source Code of this example. You can see only few lines for building a CLI tool.