Accept input via stdin and arguments in a command line application in node.js

read_arguments.js

#!/usr/bin/env node

main();

function main() {
    const usageMsg = 'Usage: ...\n';

    // If no STDIN and no arguments
    if (process.stdin.isTTY && process.argv.length <= 2) {
        process.stderr.write(usageMsg);
        process.exit(1);
    }
    // If no STDIN but arguments given
    else if (process.stdin.isTTY && process.argv.length > 2) {
        handleInput('argument', process.argv[2]);
    }
    // read from STDIN
    else {
        let data = '';
        process.stdin.on('readable', () => {
            data += process.stdin.read() || '';
        });
        process.stdin.on('end', () => {
            handleInput('stdin', data);
        });
    }
}

function handleInput(type, data) {
    console.log(type, data);
}

usage.txt

$ echo bob | node read_arguments.js
bob

$ node read_arguments.js bob
bob

$ node read_arguments.js
Usage: filename <input>