> ## Documentation Index
> Fetch the complete documentation index at: https://upstash.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# FUNCTION LOAD

> Load a library.

Use `FUNCTION LOAD` to register a library of functions in the database.

The payload is the library source code. It must begin with a shebang line naming the engine and the library, such as `#!lua name=mylib`, and register each function with `redis.register_function`, giving it a name, a callback, and optional flags such as `no-writes`. The reply is the library name.

`allow-key-locking` is one of those flags. It opts a function out of the global lock so that a call locks the [hash tag](/docs/redis/features/key-locking#hash-tags) of each key passed in its key list, which lets calls on disjoint [hash tags](/docs/redis/features/key-locking#hash-tags) run in parallel. Unlike Lua scripts, where the flag goes on the shebang line, it is declared per function in `redis.register_function`, and it is fixed until the library is loaded again. See [Key-Based Locking](/docs/redis/features/key-locking).

Whether or not you set that flag, write functions so that every key they touch arrives in the key list rather than being assembled from `ARGV` inside the function, since an undeclared key can force a disk read while the lock is held. See [Dynamic Keys and Latency](/docs/redis/features/key-locking#dynamic-keys-and-latency).

Loading fails when the library name is already in use unless `REPLACE` is given, which is how you deploy a new version of a library. Once loaded, functions are called by name with [`FCALL`](/docs/redis/commands/functions/fcall) or [`FCALL_RO`](/docs/redis/commands/functions/fcall-ro). Unlike scripts cached by [`SCRIPT LOAD`](/docs/redis/commands/scripting/script-load), libraries are part of the dataset, so they survive restarts and do not need to be re-sent by clients.

## Syntax

```redis theme={"system"}
FUNCTION LOAD [REPLACE] <function-code>
```

## Arguments

| Argument          | Required | Repeatable | Description                                                   |
| ----------------- | -------- | ---------- | ------------------------------------------------------------- |
| `REPLACE`         | No       | No         | Allow replacement of an existing destination.                 |
| `<function-code>` | Yes      | No         | Library source, including its `#!lua name=<library>` shebang. |

## Response

The reply reports the result of the operation. Error replies have the same shape in RESP2 and RESP3 and are surfaced as exceptions by the SDKs below.

| Protocol | Reply       |
| -------- | ----------- |
| RESP2    | Bulk string |
| RESP3    | Bulk string |

<Note>
  Client libraries often decode bulk strings, maps, sets, and numeric strings into language-native values. The table describes the Redis wire reply.
</Note>

## Examples

TCP examples use the TLS `REDIS_URL` from the Upstash console. REST examples use `UPSTASH_REDIS_REST_URL` and `UPSTASH_REDIS_REST_TOKEN`.

<AccordionGroup>
  <Accordion title="Redis CLI" icon="terminal">
    ```bash theme={"system"}
    FUNCTION LOAD "#!lua name=mylib\nredis.register_function('helloworld', function() return 'Hello World!' end)"
    ```
  </Accordion>

  <Accordion title="@upstash/redis" icon="node-js" iconType="brands">
    ```ts theme={"system"}
    import { Redis } from "@upstash/redis";

    const redis = Redis.fromEnv();

    const code = `#!lua name=mylib

      -- Simple function that returns a string
      redis.register_function(
        'helloworld',
        function() return 'Hello World!' end
      )

      -- Complex function that modifies data with logic
      local function my_hset(keys, args)
        local hash = keys[1]
        local time = redis.call('TIME')[1]
        return redis.call('HSET', hash, '_last_modified_', time, unpack(args))
      end

      redis.register_function('my_hset', my_hset)
    `;

    const libraryName = await redis.functions.load({ code, replace: true });

    console.log(libraryName); // "mylib"
    ```
  </Accordion>

  <Accordion title="upstash_redis" icon="python" iconType="brands">
    <Note>
      This command is not supported yet in `upstash_redis`.
    </Note>
  </Accordion>

  <Accordion title="ioredis" icon="node-js" iconType="brands">
    ```ts theme={"system"}
    import Redis from "ioredis";

    const redis = new Redis(process.env.REDIS_URL!);
    const result = await redis.function("LOAD", "function-code");
    console.log(result);
    ```
  </Accordion>

  <Accordion title="node-redis" icon="node-js" iconType="brands">
    ```ts theme={"system"}
    import { createClient } from "redis";

    const client = await createClient({ url: process.env.REDIS_URL })
      .on("error", console.error)
      .connect();
    const result = await client.functionLoad("function-code");
    console.log(result);
    ```
  </Accordion>

  <Accordion title="redis-py" icon="python" iconType="brands">
    ```python theme={"system"}
    import os
    import redis

    client = redis.from_url(os.environ["REDIS_URL"])
    result = client.function_load("function-code")
    print(result)
    ```
  </Accordion>

  <Accordion title="go-redis" icon="golang" iconType="brands">
    ```go theme={"system"}
    package main

    import (
        "context"
        "fmt"
        "os"

        "github.com/redis/go-redis/v9"
    )

    func main() {
        opts, err := redis.ParseURL(os.Getenv("REDIS_URL"))
        if err != nil {
            panic(err)
        }
        client := redis.NewClient(opts)
        result, err := client.FunctionLoad(context.Background(), "function-code").Result()
        if err != nil {
            panic(err)
        }
        fmt.Println(result)
    }
    ```
  </Accordion>

  <Accordion title="jedis" icon="java" iconType="brands">
    ```java theme={"system"}
    import java.net.URI;

    import redis.clients.jedis.Jedis;

    try (Jedis jedis = new Jedis(new URI(System.getenv("REDIS_URL")))) {
      Object result = jedis.functionLoad("function-code");
      System.out.println(result);
    }
    ```
  </Accordion>

  <Accordion title="redis-rs" icon="rust" iconType="brands">
    ```rust theme={"system"}
    fn main() -> redis::RedisResult<()> {
        let url = std::env::var("REDIS_URL").expect("REDIS_URL is not set");
        let client = redis::Client::open(url)?;
        let mut connection = client.get_connection()?;

        let mut command = redis::cmd("FUNCTION");
        command.arg("LOAD");
        command.arg("function-code");
        let result: redis::Value = command.query(&mut connection)?;
        println!("{result:?}");
        Ok(())
    }
    ```
  </Accordion>
</AccordionGroup>


## Related topics

- [FUNCTION LOAD](/docs/redis/sdks/ts/commands/functions/load.md)
- [Overview](/docs/redis/sdks/ts/commands/overview.md)
- [FCALL](/docs/redis/commands/functions/fcall.md)
- [Key-Based Locking](/docs/redis/features/key-locking.md)
- [Changelog](/docs/redis/overall/changelog.md)