Batch rename files (using regex with capture group)

rename_files.js

// this script does not handle file suffix for you
// as some files have multiple suffix segments, e.g: *.sc.ass & *.tc.ass are two common subtitle formats
// instead, you should manually specify suffix in regex as the last capture group

const fs = require("fs")

const isDryrun = !process.argv.includes("-r");

if (isDryrun) {
	console.log("Note: By default, this script will only dry run, specify -r if you want to actually run it.")
}

function getNewFilename(filename, regex, replaceWith) {
	if (!filename || !filename.match(regex)) {
		return filename
	}
	return filename.replace(re, replaceWith);
}

// rename file names in the current directory (using regex capture group)
function renameFiles(regex, replaceWith) {
	const files = fs.readdirSync(__dirname).filter(filename => filename.match(re))
	console.log(`${files.length} files matched`)
	files.forEach(file => {
		const newFile = getNewFilename(file, regex, replaceWith)
		if (isDryrun) {
		 	console.log(file, "->", newFile)
		} else {
			fs.rename(file, newFile, () => {
				console.log(`${file} -> ${newFile}`)
			})
		}
	})
}

/*
suppose under current folder, files are like:
[BeanSub&FZSD&VCB-Studio] Kimetsu no Yaiba [01][Ma10p_1080p][x265_flac_aac].mkv
[BeanSub&FZSD&VCB-Studio] Kimetsu no Yaiba [02][Ma10p_1080p][x265_flac_aac].mkv
[BeanSub&FZSD&VCB-Studio] Kimetsu no Yaiba [03][Ma10p_1080p][x265_flac_aac].mkv

and you want to rename them into:
EP01.mkv
EP02.mkv
EP03.mkv

then you can do:
const re = /^\[BeanSub.*Kimetsu no Yaiba \[([0-9][0-9])\].*(\.mkv)$/;
renameFiles(re, "EP$1$2") // $n means the nth capture group in regex
*/