Node.js - Read command line arguments (2024)

In this tutorial, we will learn easy and flexible way to read the command line argument in Node.js application.

Q: What is process.argv in node.js?
Ans:

The process.argv property contains an array that included the command-line arguments passed when the Node.js process was initiated.

console.log(process.argv)

output:

There are three strings, two of which are always supplied by node.js process.

1. The first value - process.argv[0] is the path to node executable of user machine.
2. The second value - process.argv[1] is the path to user's application file.
3. Remaining values - process.argv[2],..[n] would user provided arguments.

node student-app.js add --studentName="Joe" --address="abc"

If we are supplying action or more options/values as a command line argument, it would be simple to use yargs instead of accessing each argument by array index using process.argv[2],..[n].

Q: What is yargs in node.js?
Ans:

Yargs allows to create customized command line tools, through arguments and generating an elegant user interface. This module makes command-line arguments more dynamic and user-friendly.

Import NPM modules

1. Create new folder for the project and open it in Visual Studio Editor.
2. You can install Visual Studio Editor.

3. Create new file student-app.js under the project or while executing below npm command will point to default file called index.js
4. The npm init command will install or create the package.json file if you run it as follows.

   D:\nodejs\file-example>npm init
   This utility will walk you through creating a package.json file.
   It only covers the most common items, and tries to guess sensible defaults.
   
   See `npm help init` for definitive documentation on these fields
   and exactly what they do.
   
   Use `npm install <pkg>` afterwards to install a package and
   save it as a dependency in the package.json file.
   
   Press ^C at any time to quit.
   package name: (file-example)
   version: (1.0.0)
   description: Nodejs read argument from command line example
   entry point: (student-app.js)
   test command:
   git repository:
   keywords:
   author: techgeeknext
   license: (ISC)
   About to write to D:\nodejs\file-example\package.json:
   
   {
     "name": "file-example",
     "version": "1.0.0",
     "description": "Nodejs read argument from command line example",
     "main": "student-app.js",
     "scripts": {
       "test": "echo \"Error: no test specified\" && exit 1"
     },
     "author": "techgeeknext",
     "license": "ISC"
   }
   
   
   Is this OK? (yes) yes

Project Structure

Install Yargs dependencies

1. Go to https://www.npmjs.com/ and search Yargs.
2. You can see it'll navigate to Yargs Page, where you can find the command to install yargs dependencies and if you scroll down further you can see more details how to use the yargs in Node js.
3. Now execute npm i yargs command to install all it's dependencies modules.

   D:\nodejs\file-example>npm i yargs
   
   added 16 packages, and audited 17 packages in 3s
   
   2 packages are looking for funding
     run `npm fund` for details
   
   found 0 vulnerabilities
   

4. package.json will be updated with yargs dependency.

   {
       "name": "file-example",
       "version": "1.0.0",
       "description": "Nodejs read argument from command line example",
       "main": "student-app.js",
       "scripts": {
           "test": "echo \"Error: no test specified\" && exit 1"
       },
       "author": "techgeeknext",
       "license": "ISC",
       "dependencies": {
           "yargs": "^17.5.1"
       }
   }

Node.js Yargs

Import the yargs dependency in the student-app.js file to access the command line arguments.

const yargs = require('yargs')

console.log(yargs.argv)

output:

Now execute the below command with arguments as below:

node student-app.js add --studentName="Joe" --address="abc"

The executed file name will be displayed in the value with the dollar symbol. The only thing left would be our value, which would be supplied as an argument.

Yargs command Example

If we need to use the first parameter as an action for our application, we may do so with yargs.command as follows.

const yargs = require('yargs')

//console.log(process.argv)

yargs.command({
    command: 'add',
    describe: 'Add new student',
    handler(argv) {
        console.log("Added Student "+ argv.studentName+" with address "+argv.address)
    }
})

yargs.parse()

Run the Node.js yargs Example

Execute the node student-app.js add --studentName="Joe" --address="abc" command in the terminal to view the output.