Replace word with new word of the same length preserving case

rkc.js

#!/usr/bin/env node

const fs = require('fs');

// https://stackoverflow.com/a/17265031
function matchCase(target, pattern) {
	var result = '';

	for (var i = 0; i < target.length; i++) {
		var c = target.charAt(i);
		var p = pattern.charAt(i);

		if (/[A-Z]/.test(p)) {
			result += c.toUpperCase();
		} else {
			result += c.toLowerCase();
		}
	}

	return result;
}

const pattern = process.argv[2];
const replacement = process.argv[3];

process.argv.slice(4).forEach((file) => {
	const src = fs.readFileSync(file, 'utf8');
	const output = src.replace(new RegExp(pattern, 'gi'), match => matchCase(replacement, match));
	fs.writeFileSync(file, output, 'utf8');
	console.log("written %s", file);
});