# 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](/redis/features/key-locking#hash-tags) of each key passed in its key list, which lets calls on disjoint [hash tags](/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](/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](/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`](/redis/commands/functions/fcall) or [`FCALL_RO`](/redis/commands/functions/fcall-ro). Unlike scripts cached by [`SCRIPT LOAD`](/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
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
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
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
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
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
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
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
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
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>