# How to run a script build time in Next.js

> Learn how to run a script at build time in Next.js by adding a postbuild entry to your package.json scripts that runs a Node file after next build.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2022-05-23 | Topics: [Next.js](https://flaviocopes.com/tags/next/) | Canonical: https://flaviocopes.com/nextjs-run-script-build-time/

I was trying to see if moving my blog (based on Hugo) to [Next.js](https://flaviocopes.com/nextjs/) was a good move (it wasn't) and I found a problem.

I had to change the path of each of my images because Hugo allows a post to be in the same folder as the markdown file, while Next.js does not.

But I didn't want to disrupt my workflow. It's so nice that I can get my images in the same folder as the markdown file. It's very easy for authoring and maintenance.

So I got this plan: at build time I'd go through all the posts, gather the images, and create a folder for each of the posts in `/public/images`.

I had to change each image path in the markdown, and that was the easiest thing.

Then I had to run a post-build command by creating a `postbuild.mjs` file whose job was to go through my `content/posts` folder, and copy each image in `public/images`:

```js
import fs from 'fs'
import path from 'path'
import fsExtra from 'fs-extra'

const source = './content/posts'
const destination = './public/images'

const posts = fs.readdirSync(source)

fsExtra.emptyDirSync(destination)

fs.mkdir(destination, () => {
  posts.map((slug) => {
    if (slug === '.DS_Store') return

    fs.mkdir(`${destination}/${slug}`, () => {
      fs.readdirSync(`${source}/${slug}`)
        .filter((item) =>
          ['.png', '.jpg', '.jpeg', '.gif'].includes(path.extname(item))
        )
        .map((item) => {
          fs.copyFile(
            `${source}/${slug}/${item}`,
            `${destination}/${slug}/${item.replace(/ /g, '-')}`,
            () => {
              console.log(`${destination}/${slug}/${item}`)
            }
          )
        })
    })
  })
})
```

Then add a `postbuild` entry in your `package.json` file `scripts`:

```json
{
  ...
  "scripts": {
    "build": "next build",
    "postbuild": "node ./postbuild.mjs",
    "dev": "next dev",
    "start": "next start",
    ...
  }
}
```

Using the same technique you could create a `prebuild` entry that's run before the build.

By the way this is not unique to Next.js, it's a feature of [npm](https://flaviocopes.com/npm/). See https://docs.npmjs.com/cli/v6/using-npm/scripts#pre--post-scripts.