# How to mass rename files in Node.js

> Learn how to mass rename a set of files in Node.js with the fs module, using readdirSync, mkdirSync, and renameSync to move each file into its own folder.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2020-04-11 | Updated: 2022-04-20 | Topics: [Node.js](https://flaviocopes.com/tags/node/) | Canonical: https://flaviocopes.com/node-mass-rename-files/

In this blog post I'm going to explain how to rename a set of files.

The same process works to move files to another folder, because when you rename you rename the path of the file.

The motivation for this task was this: in Hugo we can write blog posts as files, like this:

```
first-post.md
second-post.md
third-post.md
```

We can also add them to a folder that contains an `index.md` file:

```
first-post/
  > index.md
second-post/
  > index.md
third-post/
  > index.md
```

The difference is that with folder we can add images and associate them more easily to a blog post.

I could have done the change manually, but I had about 50 files in the folder and I didn't really want to do that job.

I wanted it to happen automatically.

Let's start by requiring one core module we're going to use: `fs`. As it is a core module, there's no need to `npm install` it.

```js
const fs = require('fs')
```

Then, get a reference to the current folder. I suppose we're going to run the script in the same folder where we want to perform this change.

`__dirname` is the variable that always points to the current working folder.

I get a list of all the files and folders:

```js
const files = fs.readdirSync(__dirname)
```

Then I filter out only the items that end with `.md`:

```js
for (const file of files) {
  if (file.endsWith('.md')) {
    console.log(file)
  }
}
```

Once we have the `file` reference, which represents the filename, we can call `fs.mkdirSync()` to create the folder:

```js
fs.mkdirSync(
  __dirname + '/' + file.replace('.md', ''),
  { recursive: true },
  (err) => {
    console.log(err)
  }
)
```

Once we create the folder, we call `fs.renameSync()`.

The reason I us the **blocking versions** `mkdirSync()` and `renameSync()` instead of `mkdir()` and `rename()` is that I want to wait until the folder is created before moving the file to the folder. Otherwise we might get errors if the second function runs before the second (I'd use `await` but the [Node.js](https://flaviocopes.com/nodejs/) API does not use promises, we'd have to use [promisify](https://flaviocopes.com/node-promisify/) but it's simpler to use the blocking version of those APIs).

The `fs.renameSync()` function accepts 3 parameters:

1. the current path
2. the path we want to move to
3. an callback fired if there's an error

The current path is:

```js
__dirname + '/' + file
```

The path we want to move to is:

```js
__dirname + '/' + file.replace('.md', '') + '/index.md'
```

See? We create a new folder from the file name, then we append `index.md`:

```js
fs.renameSync(
  __dirname + '/' + file,
  __dirname + '/' + file.replace('.md', '') + '/index.md',
  err => {
    console.log(err)
  }
)
```

Here's the full code:

```js
const fs = require('fs')
const files = fs.readdirSync(__dirname)

for (const file of files) {
  if (file.endsWith('.md')) {
    fs.mkdirSync(
      __dirname + '/' + file.replace('.md', ''),
      { recursive: true },
      (err) => {
        console.log(err)
      }
    )

    fs.renameSync(
      __dirname + '/' + file,
      __dirname + '/' + file.replace('.md', '') + '/index.md',
      (err) => {
        console.log(err)
      }
    )
  }
}
```