---
title: "fd_dup()"
description: "The fd_dup() function duplicates a file handle, creating a new file handle that is a duplicate of the original. The duplicated file handle refers to the same underlying file or resource as the original file handle."
url: "https://wasix.org/docs/api-reference/wasix/fd_dup/"
markdown: "https://wasix.org/docs/api-reference/wasix/fd_dup.md"
---

# `fd_dup()`

Duplicates a file handle.

## Description

The `fd_dup()` function duplicates a file handle, creating a new file handle that is a duplicate of the original. The duplicated file handle refers to the same underlying file or resource as the original file handle.

## Syntax

```ebnf
  (@interface func (export "fd_dup")
    (param $fd $fd)
    (result $error (expected $fd (error $errno)))
  )
```

## Parameters

- `ctx`: A mutable reference to the function environment.
- `fd`: The file handle to be cloned.
- `ret_fd`: A WebAssembly memory pointer where the new file handle will be stored.

## Return Value

The function returns an `Errno` value indicating the success or failure of the operation.

## Logging

This function has been instrumented with debug-level logging. It will log the following information:

- `%fd`: The file handle being duplicated.
- `ret_fd`: The new file handle that is a duplicate of the original.

## Note

The `fd_dup()` function duplicates a file handle. It takes the file handle `fd` to be cloned and a WebAssembly memory pointer `ret_fd` where the new file handle will be stored.

The function retrieves the memory view and the file system state from the WASI environment using the function context. It then calls the `clone_fd()` method on the file system state to duplicate the file handle. The `clone_fd()` method creates a new file handle that is a duplicate of the original file handle.

The duplicated file handle is stored in the WebAssembly memory using the provided memory pointer `ret_fd`.

The function returns an `Errno` value to indicate the success or failure of the operation. If the file handle is successfully duplicated, it returns `Errno::Success`. Otherwise, it returns an appropriate error code.

---

[Documentation index](https://wasix.org/llms.txt) · [HTML version](https://wasix.org/docs/api-reference/wasix/fd_dup/)