Hello World command line

Node.js can 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 a Unix System:

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

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

#!/usr/bn/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 Dragon && ls -> will execute ls 
    process.exit(1);
}


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