---
title: "open( filePath, [mode] ) | Grafana k6 documentation"
description: "Opens a file and reads all the contents into memory."
---

# open( filePath, \[mode] )

Opens a file, reading all its contents into memory for use in the script.

> Caution
> 
> `open()` can only be called from the [init context](/docs/k6/latest/using-k6/test-lifecycle/#the-init-stage). This restriction is necessary to determine the local files needed to bundle when distributing the test across multiple nodes.

> Note
> 
> `open()` often consumes a large amount of memory because every VU keeps a separate copy of the file in memory.
> 
> To reduce the memory consumption, you can:
> 
> - Use `open()` within a [SharedArray](/docs/k6/latest/javascript-api/k6-data/sharedarray/), which shares the allocated file memory between VUs.
> - Use [open() from the `k6/experimental/fs`](/docs/k6/latest/javascript-api/k6-experimental/fs/) module. It provides a memory-efficient way to handle file interactions in your test script and can read files in small chunks.

Expand table

| Parameter | Type   | Description                                                                                                                                       |
|-----------|--------|---------------------------------------------------------------------------------------------------------------------------------------------------|
| filePath  | string | The path to the file, absolute or relative, that will be read into memory. The file will only be loaded once, even when running with several VUs. |
| mode      | string | By default, the contents of the file are read as text, but if you specify `b`, the file will be read as binary data instead.                      |

### Returns

Expand table

| Type                 | Description                                                                                     |
|----------------------|-------------------------------------------------------------------------------------------------|
| string / ArrayBuffer | The contents of the file, returned as string or ArrayBuffer (if `b` was specified as the mode). |

### Examples

JSON ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```json
[
  {
    "username": "user1",
    "password": "password1"
  },
  {
    "username": "user2",
    "password": "password2"
  },
  {
    "username": "user3",
    "password": "password3"
  }
]
```

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
import { SharedArray } from 'k6/data';
import { sleep } from 'k6';

const data = new SharedArray('users', function () {
  // here you can open files, and then do additional processing or generate the array with data dynamically
  const f = JSON.parse(open('./users.json'));
  return f; // f must be an array[]
});

export default () => {
  const randomUser = data[Math.floor(Math.random() * data.length)];
  console.log(`${randomUser.username}, ${randomUser.password}`);
  sleep(3);
};
```

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
import { sleep } from 'k6';

const users = JSON.parse(open('./users.json')); // consider using SharedArray for large files

export default function () {
  const user = users[__VU - 1];
  console.log(`${user.username}, ${user.password}`);
  sleep(3);
}
```

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
import http from 'k6/http';
import { sleep } from 'k6';

const binFile = open('/path/to/file.bin', 'b');

export default function () {
  const data = {
    field: 'this is a standard form field',
    file: http.file(binFile, 'test.bin'),
  };
  const res = http.post('https://example.com/upload', data);
  sleep(3);
}
```