How do I pass command line arguments to a Node.js program and receive them?

To pass command line arguments to a Node.js program and access them, you can use the built-in process.argv array or leverage libraries like yargs or commander for structured parsing. Here’s how:

1. Basic Method: Using process.argv

The process.argv array contains command line arguments provided when running the script.
Indexes:

• 0: Path to the Node.js executable.
• 1: Path to the script file.
• 2+: User-provided arguments.

Example:

// script.js
const args = process.argv.slice(2); // Extract user arguments
console.log("Arguments:", args);

Run:

node script.js arg1 arg2 --input=file.txt

Output:

Arguments: [ 'arg1', 'arg2', '--input=file.txt' ]

2. Structured Parsing with Libraries

A. Using yargs (Recommended)

Install:

npm install yargs

Example:

const yargs = require('yargs/yargs');
const { argv } = yargs(process.argv.slice(2))
  .option('input', {
    alias: 'i',
    type: 'string',
    description: 'Input file path'
  })
  .option('verbose', {
    alias: 'v',
    type: 'boolean',
    description: 'Enable verbose logging'
  });

console.log("Input file:", argv.input);
console.log("Verbose mode:", argv.verbose);

Run:

node script.js --input=data.csv --verbose

Output:

Input file: data.csv
Verbose mode: true

B. Using commander

Install:

npm install commander

Example:

const { program } = require('commander');

program
  .name('my-script')
  .description('CLI tool to process data')
  .option('-i, --input <file>', 'Input file')
  .option('-v, --verbose', 'Enable verbose mode');

program.parse(process.argv);
const options = program.opts();

console.log("Input file:", options.input);
console.log("Verbose mode:", options.verbose);

Run:

node script.js -i data.csv -v

3. Handling Positional Arguments

Use .command() in yargs to define positional arguments:

const argv = require('yargs/yargs')(process.argv.slice(2))
  .command('<input> [output]', 'Process input and save to output')
  .parse();

console.log("Input:", argv._[0]);
console.log("Output:", argv._[1]);

Run:

node script.js input.txt output.txt

Key Differences

Method	Pros	Cons
process.argv	No dependencies, simple for basic use.	Manual parsing for complex cases.
yargs/commander	Auto-parsing, validation, help menus.	Adds dependencies.

Best Practices

1. Validate Inputs: Ensure arguments meet expected formats.
2. Sanitize Values: Prevent security issues like path traversal.
3. Use Help Menus: Libraries like commander auto-generate --help.

Choose process.argv for trivial cases and libraries like yargs/commander for complex CLI tools!