Node.js Getting started with Node.js Hello World command line


Example

Node.js can also be used to create command line utilities. The example below reads the first argument from the command line and prints a Hello message.

To run this code on an Unix System:

  1. Create a new file and paste the code below. The filename is irrelevant.
  2. Make this file executable with chmod 700 FILE_NAME
  3. Run the app with ./APP_NAME David

On Windows you do step 1 and run it with node APP_NAME David

#!/usr/bin/env node

'use strict';

/*
    The command line arguments are stored in the `process.argv` array, 
    which has the following structure:
    [0] The path of the executable that started the Node.js process
    [1] The path to this application
    [2-n] the command line arguments

    Example: [ '/bin/node', '/path/to/yourscript', 'arg1', 'arg2', ... ]
    src: https://nodejs.org/api/process.html#process_process_argv
 */

// Store the first argument as username.
var username = process.argv[2];

// Check if the username hasn't been provided.
if (!username) {

    // Extract the filename
    var appName = process.argv[1].split(require('path').sep).pop();

    //  Give the user an example on how to use the app.
    console.error('Missing argument! Example: %s YOUR_NAME', appName);

    // Exit the app (success: 0, error: 1). 
    // An error will stop the execution chain. For example:
    //   ./app.js && ls       -> won't execute ls
    //   ./app.js David && ls -> will execute ls
    process.exit(1);
}

// Print the message to the console.
console.log('Hello %s!', username);