---
title: extern
categories: |
  core
version: 0.104.0
core: |
  Define a signature for an external command.
usage: |
  Define a signature for an external command.
editLink: false
contributors: false
---
<!-- This file is automatically generated. Please edit the command in https://github.com/nushell/nushell instead. -->

# `extern` for [core](/commands/categories/core.md)

<div class='command-title'>Define a signature for an external command.</div>

## Signature

```> extern {flags} (def_name) (params)```

## Parameters

 -  `def_name`: Definition name.
 -  `params`: Parameters.


## Input/output types:

| input   | output  |
| ------- | ------- |
| nothing | nothing |
## Examples

Write a signature for an external command
```nu
> extern echo [text: string]

```

## Notes
This command is a parser keyword. For details, check:
  https://www.nushell.sh/book/thinking_in_nu.html