---
url: /process-functions/datasource-writeFile.md
description: Writes data to a file in the MODLR file system.
---

# datasource.writeFile 

Writes data to a file in the MODLR file system. Creates parent directories if they don't exist. The file must be within the root directory of the datasource.

```js
datasource.writeFile(fileName, data, append)
```

#### Parameters

* `fileName` - The name and file path of the file in the MODLR file system to write to. File path can be found in the filesystem page.
* `data` - The data to write to the file. Supported types:
  * `String` - Written as UTF-8 encoded text
  * `int[]` - Array of integers, each value masked to a single byte (0-255)
  * `byte[]` - Written directly to the file
  * `List` - List of numbers, converted to bytes
* `append` (optional) - If `true`, appends data to the end of the file. If `false` or omitted, overwrites the file. Defaults to `false`.

#### Returns

* `boolean` - Returns `true` if the file was written successfully, `false` if the file path is invalid.

#### Example

```js
// Write text to a new file
datasource.writeFile("output/report.txt", "Hello, World!");

// Append text to an existing file
datasource.writeFile("output/log.txt", "New log entry\n", true);

// Write binary data as an array of integers
let bytes = [72, 101, 108, 108, 111]; // "Hello" in ASCII
datasource.writeFile("output/data.bin", bytes);

// Write JSON data
let data = {
    name: "Budget Report",
    year: 2024,
    values: [100, 200, 300]
};
datasource.writeFile("output/report.json", JSON.stringify(data, null, 2));
```