# FUNCTION LOAD Load a library to Redis. The command's gets a single mandatory parameter which is the source code that implements the library. The library payload must start with Shebang statement that provides a metadata about the library (like the engine to use and the library name). Shebang format: `#! name=`. Currently engine name must be `lua`. For the Lua engine, the implementation should declare one or more entry points to the library with the [`redis.register_function()` API](https://redis.io/docs/latestdevelop/interact/programmability/lua-api#redis.register_function). Once loaded, you can call the functions in the library with the [`FCALL`](https://redis.io/docs/latest/commands/fcall) (or [`FCALL_RO`](https://redis.io/docs/latest/commands/fcall_ro) when applicable) command. When attempting to load a library with a name that already exists, the Redis server returns an error. The `REPLACE` modifier changes this behavior and overwrites the existing library with the new contents. The command will return an error in the following circumstances: * An invalid _engine-name_ was provided. * The library's name already exists without the `REPLACE` modifier. * A function in the library is created with a name that already exists in another library (even when `REPLACE` is specified). * The engine failed in creating the library's functions (due to a compilation error, for example). * No functions were declared by the library. For more information please refer to [Introduction to Redis Functions](https://redis.io/docs/latest/develop/interact/programmability/functions-intro). ## Examples The following example will create a library named `mylib` with a single function, `myfunc`, that returns the first argument it gets. ``` redis> FUNCTION LOAD "#!lua name=mylib \n redis.register_function('myfunc', function(keys, args) return args[1] end)" mylib redis> FCALL myfunc 0 hello "hello" ``` ## Return information {{< multitabs id="function-load-return-info" tab1="RESP2" tab2="RESP3" >}} [Bulk string reply](../../develop/reference/protocol-spec#bulk-strings): the library name that was loaded. -tab-sep- [Bulk string reply](../../develop/reference/protocol-spec#bulk-strings): the library name that was loaded.