---
description: Load and use Jawk extensions from the CLI or the Java API.
date_published: 2026-05-13
date_modified: 2026-05-13
canonical_url: https://jawk.io/extensions.html
---

# Using Extensions

On this Page

- [How Extensions Are Enabled](#how-extensions-are-enabled)
- [List Available Extensions](#list-available-extensions)
- [Load Extensions from the CLI](#load-extensions-from-the-cli)
- [Load Extensions from Java](#load-extensions-from-java)
- [Built-In Extensions](#built-in-extensions)
- [Sandbox Interaction](#sandbox-interaction)
- [See Also](#see-also)

Jawk extensions let Java code expose additional AWK-callable functions to a script. Extensions are never enabled automatically. The host application or CLI invocation decides exactly which extension instances are available.

** Important

Extensions are opt-in. Sandbox mode blocks dynamic extension loading during script execution, but preloading an extension through the CLI or the Java host remains an explicit host decision.

## [How Extensions Are Enabled](#how-extensions-are-enabled)

There are two supported loading paths:

- CLI: `-l <extension>` or `--load <extension>`
- Java API: pass extension instances to an `Awk` constructor

If you do neither, no extension functions are available.

## [List Available Extensions](#list-available-extensions)

From the CLI, print the currently registered extension identifiers:

```shell-session
$ java -jar jawk-6.4.00-standalone.jar --list-ext
```

From Java, inspect the registry directly:

```java
Awk.listAvailableExtensions().forEach((name, extension) ->
        System.out.println(name + " -> " + extension.getClass().getName()));
```

The registry may expose multiple identifiers for the same implementation, for example a registered name, a simple class name, and a fully qualified class name.

## [Load Extensions from the CLI](#load-extensions-from-the-cli)

Load an extension with any supported identifier:

```shell-session
$ java -jar jawk-6.4.00-standalone.jar -l stdin -f script.awk
```

```shell-session
$ java -jar jawk-6.4.00-standalone.jar -l io.jawk.ext.StdinExtension -f script.awk
```

If the extension class is not already registered, the CLI can still resolve it by fully qualified class name as long as the class is available on the JVM classpath.

## [Load Extensions from Java](#load-extensions-from-java)

Pass extension instances directly to `Awk`:

```java
Awk awk = new Awk(StdinExtension.INSTANCE, new MyExtension());
```

That keeps extension availability explicit and local to the embedding code.

## [Built-In Extensions](#built-in-extensions)

The current built-in registry includes the stdin extension, which is exposed through identifiers such as:

- `stdin`
- `StdinExtension`
- `io.jawk.ext.StdinExtension`

That extension provides advanced helper functions including `StdinHasInput()`, `StdinGetline()`, and `StdinBlock()`.

## [Sandbox Interaction](#sandbox-interaction)

Sandboxing and extensions are separate concerns:

- sandboxing restricts dangerous AWK runtime features
- extension loading is still an explicit host choice
- scripts do not get to expand their own capabilities automatically

If you need a sandboxed Java embedding, construct `SandboxedAwk` with the extension instances you want to allow. If you need a sandboxed CLI run, combine `-S` with the `-l` options you want to preload.

## [See Also](#see-also)

- [Writing Extensions](extensions-writing.html)[1]
- [Java Quickstart](java.html)[2]
- [CLI Basics](cli.html)[3]