> ## 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.

## Examples

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

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

> **@upstash/redis**
>
> ```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"
> ```

> **upstash\_redis**
>
> > [!NOTE]
> >
> > This command is not supported yet in `upstash_redis`.

> **ioredis**
>
> ```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);
> ```

> **node-redis**
>
> ```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);
> ```

> **redis-py**
>
> ```python theme={"system"}
> import os
> import redis
>
> client = redis.from_url(os.environ["REDIS_URL"])
> result = client.function_load("function-code")
> print(result)
> ```

> **go-redis**
>
> ```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)
> }
> ```

> **jedis**
>
> ```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);
> }
> ```

> **redis-rs**
>
> ```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(())
> }
> ```


## 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)


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