Valkey Lua API reference

This page is under review. The page is likely incorrect, contains invalid links, and/or needs technical review. In the future it may change substantially or be removed entirely.

Valkey includes an embedded Lua 5.1 interpreter. The interpreter runs user-defined ephemeral scripts and functions. Scripts run in a sandboxed context and can only access specific Lua packages. This page describes the packages and APIs available inside the execution's context.

Sandbox context

The sandboxed Lua context attempts to prevent accidental misuse and reduce potential threats from the server's environment.

Scripts should never try to access the Valkey server's underlying host systems. That includes the file system, network, and any other attempt to perform a system call other than those supported by the API.

Scripts should operate solely on data stored in Valkey and data provided as arguments to their execution.

Global variables and functions

The sandboxed Lua execution context blocks the declaration of global variables and functions. The blocking of global variables is in place to ensure that scripts and functions don't attempt to maintain any runtime context other than the data stored in Valkey. In the (somewhat uncommon) use case that a context needs to be maintain between executions, you should store the context in Valkey' keyspace.

Valkey will return an error when trying to execute the following snippet:

my_global_variable = 'some value'

And similarly for the following global function declaration:

function my_global_function()
  -- Do something amazing
end

You'll also get a similar error when your script attempts to access any global variables that are undefined in the runtime's context:

-- The following will surely raise an error
return an_undefined_global_variable

Instead, all variable and function definitions are required to be declared as local. To do so, you'll need to prepend the local keyword to your declarations. For example, the following snippet will be considered perfectly valid by Valkey:

local my_local_variable = 'some value'

local function my_local_function()
  -- Do something else, but equally amazing
end

Note: the sandbox attempts to prevent the use of globals. Using Lua's debugging functionality or other approaches such as altering the meta table used for implementing the globals' protection to circumvent the sandbox isn't hard. However, it is difficult to circumvent the protection by accident. If the user messes with the Lua global state, the consistency of AOF and replication can't be guaranteed. In other words, just don't do it.

Imported Lua modules

Using imported Lua modules is not supported inside the sandboxed execution context. The sandboxed execution context prevents the loading modules by disabling Lua's require function.

The only libraries that Valkey ships with and that you can use in scripts are listed under the Runtime libraries section.

Runtime globals

While the sandbox prevents users from declaring globals, the execution context is pre-populated with several of these.

For some of them, a "since version" is specified. The ones without "since version" specified are available in all maintained versions.

The KEYS global variable

  • Available in scripts: yes
  • Available in functions: no

Important: to ensure the correct execution of scripts, both in standalone and clustered deployments, all names of keys that a function accesses must be explicitly provided as input key arguments. The script should only access keys whose names are given as input arguments. Scripts should never access keys with programmatically-generated names or based on the contents of data structures stored in the database.

The KEYS global variable is available only for ephemeral scripts. It is pre-populated with all key name input arguments.

The ARGV global variable

  • Available in scripts: yes
  • Available in functions: no

The ARGV global variable is available only in ephemeral scripts. It is pre-populated with all regular input arguments.

The server singleton

  • Since version: 7.2.5
  • Available in scripts: yes
  • Available in functions: yes

The server singleton is an object instance that's accessible from all scripts. It provides the API to interact with Valkey from scripts. Following is the API provided by the server object instance.

Note: For compatibility with Redis, Valkey also exposes a redis top-level object, that exposes the exact same set of APIs as the server object. Valkey does not intend to drop compatibility for this redis API, but it is recommended to use the server object for newly developed scripts.

server object fields (functions and variables)

server.call(command [,arg...])

  • Available in scripts: yes
  • Available in functions: yes

The server.call() function calls a given Valkey command and returns its reply. Its inputs are the command and arguments, and once called, it executes the command in Valkey and returns the reply.

For example, we can call the ECHO command from a script and return its reply like so:

return server.call('ECHO', 'Echo, echo... eco... o...')

If and when server.call() triggers a runtime exception, the raw exception is raised back to the user as an error, automatically. Therefore, attempting to execute the following ephemeral script will fail and generate a runtime exception because ECHO accepts exactly one argument:

127.0.0.1:6379> EVAL "return server.call('ECHO', 'Echo,', 'echo... ', 'eco... ', 'o...')" 0
(error) ERR Wrong number of args calling Valkey command from script script: b0345693f4b77517a711221050e76d24ae60b7f7, on @user_script:1.

Note that the call can fail due to various reasons, see Execution under low memory conditions and Script flags

To handle Valkey runtime errors use server.pcall() instead.

server.pcall(command [,arg...])

  • Available in scripts: yes
  • Available in functions: yes

This function enables handling runtime errors raised by the Valkey server. The server.pcall() function behaves exactly like server.call(), except that it:

  • Always returns a reply.
  • Never throws a runtime exception, and returns in its stead a server.error_reply in case that a runtime exception is thrown by the server.

The following demonstrates how to use server.pcall() to intercept and handle runtime exceptions from within the context of an ephemeral script.

local reply = server.pcall('ECHO', unpack(ARGV))
if reply['err'] ~= nil then
  -- Handle the error sometime, but for now just log it
  server.log(server.LOG_WARNING, reply['err'])
  reply['err'] = 'ERR Something is wrong, but no worries, everything is under control'
end
return reply

Evaluating this script with more than one argument will return:

127.0.0.1:6379> EVAL "..." 0 hello world
(error) ERR Something is wrong, but no worries, everything is under control

server.error_reply(x)

  • Available in scripts: yes
  • Available in functions: yes

This is a helper function that returns an error reply. The helper accepts a single string argument and returns a Lua table with the err field set to that string.

The outcome of the following code is that error1 and error2 are identical for all intents and purposes:

local text = 'ERR My very special error'
local reply1 = { err = text }
local reply2 = server.error_reply(text)

Therefore, both forms are valid as means for returning an error reply from scripts:

127.0.0.1:6379> EVAL "return { err = 'ERR My very special table error' }" 0
(error) ERR My very special table error
127.0.0.1:6379> EVAL "return server.error_reply('ERR My very special reply error')" 0
(error) ERR My very special reply error

For returning Valkey status replies refer to server.status_reply(). Refer to the Data type conversion for returning other response types.

Note: By convention, Valkey uses the first word of an error string as a unique error code for specific errors or ERR for general-purpose errors. Scripts are advised to follow this convention, as shown in the example above, but this is not mandatory.

server.status_reply(x)

  • Available in scripts: yes
  • Available in functions: yes

This is a helper function that returns a simple string reply. "OK" is an example of a standard Valkey status reply. The Lua API represents status replies as tables with a single field, ok, set with a simple status string.

The outcome of the following code is that status1 and status2 are identical for all intents and purposes:

local text = 'Frosty'
local status1 = { ok = text }
local status2 = server.status_reply(text)

Therefore, both forms are valid as means for returning status replies from scripts:

127.0.0.1:6379> EVAL "return { ok = 'TICK' }" 0
TICK
127.0.0.1:6379> EVAL "return server.status_reply('TOCK')" 0
TOCK

For returning Valkey error replies refer to server.error_reply(). Refer to the Data type conversion for returning other response types.

server.sha1hex(x)

  • Available in scripts: yes
  • Available in functions: yes

This function returns the SHA1 hexadecimal digest of its single string argument.

You can, for example, obtain the empty string's SHA1 digest:

127.0.0.1:6379> EVAL "return server.sha1hex('')" 0
"da39a3ee5e6b4b0d3255bfef95601890afd80709"

server.log(level, message)

  • Available in scripts: yes
  • Available in functions: yes

This function writes to the Valkey server log.

It expects two input arguments: the log level and a message. The message is a string to write to the log file. Log level can be on of these:

  • server.LOG_DEBUG
  • server.LOG_VERBOSE
  • server.LOG_NOTICE
  • server.LOG_WARNING

These levels map to the server's log levels. The log only records messages equal or greater in level than the server's loglevel configuration directive.

The following snippet:

server.log(server.LOG_WARNING, 'Something is terribly wrong')

will produce a line similar to the following in your server's log:

[32343] 22 Mar 15:21:39 # Something is terribly wrong

server.setresp(x)

  • Available in scripts: yes
  • Available in functions: yes

This function allows the executing script to switch between RESP protocol versions for the replies returned by server.call() and server.pcall(). It expects a single numerical argument as the protocol's version. The default protocol version is 2, but it can be switched to version 3.

Here's an example of switching to RESP3 replies:

server.setresp(3)

Please refer to the Data type conversion for more information about type conversions.

server.set_repl(x)

  • Available in scripts: yes
  • Available in functions: no

Note: Prior to Redis OSS 7.0, scripts were replicated verbatim by default. Since Redis OSS 7.0 (and Valkey), script effects replication is the only replication mode available.

The server.set_repl() function instructs the server how to treat subsequent write commands in terms of replication. It accepts a single input argument that only be one of the following:

  • server.REPL_ALL: replicates the effects to the AOF and replicas.
  • server.REPL_AOF: replicates the effects to the AOF alone.
  • server.REPL_REPLICA: replicates the effects to the replicas alone.
  • server.REPL_SLAVE: same as REPL_REPLICA, maintained for backward compatibility.
  • server.REPL_NONE: disables effect replication entirely.

By default, the scripting engine is initialized to the server.REPL_ALL setting when a script begins its execution. You can call the server.set_repl() function at any time during the script's execution to switch between the different replication modes.

A simple example follows:

server.replicate_commands() -- Enable effects replication in versions lower than Redis OSS v7.0
server.call('SET', KEYS[1], ARGV[1])
server.set_repl(server.REPL_NONE)
server.call('SET', KEYS[2], ARGV[2])
server.set_repl(server.REPL_ALL)
server.call('SET', KEYS[3], ARGV[3])

If you run this script by calling EVAL "..." 3 A B C 1 2 3, the result will be that only the keys A and C are created on the replicas and AOF.

server.replicate_commands()

  • Until version: 7.0.0
  • Available in scripts: yes
  • Available in functions: no

This function switches the script's replication mode from verbatim replication to effects replication. You can use it to override the default verbatim script replication mode used by Redis OSS until version 7.0.

Note: Verbatim script replication is no longer supported. The only script replication mode supported is script effects' replication. For more information, please refer to Replicating commands instead of scripts

server.breakpoint()

  • Available in scripts: yes
  • Available in functions: no

This function triggers a breakpoint when using the Valkey Lua debugger.

server.debug(x)

  • Available in scripts: yes
  • Available in functions: no

This function prints its argument in the Valkey Lua debugger console.

server.acl_check_cmd(command [,arg...])

  • Since version: 7.0.0
  • Available in scripts: yes
  • Available in functions: yes

This function is used for checking if the current user running the script has ACL permissions to execute the given command with the given arguments.

The return value is a boolean true in case the current user has permissions to execute the command (via a call to server.call or server.pcall) or false in case they don't.

The function will raise an error if the passed command or its arguments are invalid.

server.register_function

  • Since version: 7.0.0
  • Available in scripts: no
  • Available in functions: yes

This function is only available from the context of the FUNCTION LOAD command. When called, it registers a function to the loaded library. The function can be called either with positional or named arguments.

positional arguments: server.register_function(name, callback)

The first argument to server.register_function is a Lua string representing the function name. The second argument to server.register_function is a Lua function.

Usage example:

127.0.0.1:6379> FUNCTION LOAD "#!lua name=mylib\n server.register_function('noop', function() end)"

Named arguments: server.register_function{function_name=name, callback=callback, flags={flag1, flag2, ..}, description=description}

The named arguments variant accepts the following arguments:

  • function_name: the function's name.
  • callback: the function's callback.
  • flags: an array of strings, each a function flag (optional).
  • description: function's description (optional).

Both function_name and callback are mandatory.

Usage example:

127.0.0.1:6379> FUNCTION LOAD "#!lua name=mylib\n server.register_function{function_name='noop', callback=function() end, flags={ 'no-writes' }, description='Does nothing'}"

Script flags

Important: Use script flags with care, which may negatively impact if misused. Note that the default for Eval scripts are different than the default for functions that are mentioned below, see Eval Flags

When you register a function or load an Eval script, the server does not know how it accesses the database. By default, Valkey assumes that all scripts read and write data. This results in the following behavior:

  1. They can read and write data.
  2. They can run in cluster mode, and are not able to run commands accessing keys of different hash slots.
  3. Execution against a stale replica is denied to avoid inconsistent reads.
  4. Execution under low memory is denied to avoid exceeding the configured threshold.

You can use the following flags and instruct the server to treat the scripts' execution differently:

  • no-writes: this flag indicates that the script only reads data but never writes.

    By default, Valkey will deny the execution of flagged scripts (Functions and Eval scripts with shebang) against read-only replicas, as they may attempt to perform writes. Similarly, the server will not allow calling scripts with FCALL_RO / EVAL_RO. Lastly, when data persistence is at risk due to a disk error, execution is blocked as well.

    Using this flag allows executing the script:

    1. With FCALL_RO / EVAL_RO
    2. On read-only replicas.
    3. Even if there's a disk error (Valkey is unable to persist so it rejects writes).
    4. When over the memory limit since it implies the script doesn't increase memory consumption (see allow-oom below)

    However, note that the server will return an error if the script attempts to call a write command. Also note that currently PUBLISH, SPUBLISH and PFCOUNT are also considered write commands in scripts, because they could attempt to propagate commands to replicas and AOF file.

    For more information please refer to Read-only scripts

  • allow-oom: use this flag to allow a script to execute when the server is out of memory (OOM).

    Unless used, Valkey will deny the execution of flagged scripts (Functions and Eval scripts with shebang) when in an OOM state. Furthermore, when you use this flag, the script can call any Valkey command, including commands that aren't usually allowed in this state. Specifying no-writes or using FCALL_RO / EVAL_RO also implies the script can run in OOM state (without specifying allow-oom)

  • allow-stale: a flag that enables running the flagged scripts (Functions and Eval scripts with shebang) against a stale replica when the replica-serve-stale-data config is set to no .

    Valkey can be set to prevent data consistency problems from using old data by having stale replicas return a runtime error. For scripts that do not access the data, this flag can be set to allow stale Valkey replicas to run the script. Note however that the script will still be unable to execute any command that accesses stale data.

  • no-cluster: the flag causes the script to return an error in Valkey cluster mode.

    Valkey allows scripts to be executed both in standalone and cluster modes. Setting this flag prevents executing the script against nodes in the cluster.

  • allow-cross-slot-keys: The flag that allows a script to access keys from multiple slots.

    Valkey typically prevents any single command from accessing keys that hash to multiple slots. This flag allows scripts to break this rule and access keys within the script that access multiple slots. Declared keys to the script are still always required to hash to a single slot. Accessing keys from multiple slots is discouraged as applications should be designed to only access keys from a single slot at a time, allowing slots to move between Valkey servers.

    This flag has no effect when cluster mode is disabled.

Please refer to Function Flags and Eval Flags for a detailed example.

server.SERVER_VERSION

  • Since version: 7.2.5
  • Available in scripts: yes
  • Available in functions: yes

Returns the current Valkey server version as a Lua string. The reply's format is MM.mm.PP, where:

  • MM: is the major version.
  • mm: is the minor version.
  • PP: is the patch level.

server.REDIS_VERSION

  • Since version: 7.0.0
  • Available in scripts: yes
  • Available in functions: yes

Returns the current Redis compatibility version as a Lua string. The reply's format is MM.mm.PP, where:

  • MM: is the major version.
  • mm: is the minor version.
  • PP: is the patch level.

server.SERVER_VERSION_NUM

  • Since version: 7.2.5
  • Available in scripts: yes
  • Available in functions: yes

Returns the current Valkey server version as a number. The reply is a hexadecimal value structured as 0x00MMmmPP, where:

  • MM: is the major version.
  • mm: is the minor version.
  • PP: is the patch level.

server.REDIS_VERSION_NUM

  • Since version: 7.0.0
  • Available in scripts: yes
  • Available in functions: yes

Returns the current Redis compatibility version as a number. The reply is a hexadecimal value structured as 0x00MMmmPP, where:

  • MM: is the major version.
  • mm: is the minor version.
  • PP: is the patch level.

Data type conversion

Unless a runtime exception is raised, server.call() and server.pcall() return the reply from the executed command to the Lua script. Valkey's replies from these functions are converted automatically into Lua's native data types.

Similarly, when a Lua script returns a reply with the return keyword, that reply is automatically converted to RESP protocol.

Put differently: There's a one-to-one mapping between Valkey's replies and Lua's data types and a one-to-one mapping between Lua's data types and the RESP Protocol data types. The underlying design is such that if a RESP type is converted into a Lua type and converted back into a RESP type, the result is the same as the initial value.

Type conversion from Valkey replies (i.e. the replies from server.call() and server.pcall()) to Lua data types depends on the RESP protocol version used by the script. The default protocol version during script executions is RESP2. The script may switch the replies' protocol versions by calling the server.setresp() function.

Type conversion from a script's returned Lua data type depends on the user's choice of protocol (see the HELLO command).

The following sections describe the type conversion rules between Lua and Valkey per the protocol's version.

RESP2 to Lua type conversion

The following type conversion rules apply to the execution's context by default as well as after calling server.setresp(2):

Lua to RESP2 type conversion

The following type conversion rules apply by default as well as after the user had called HELLO 2:

There is an additional Lua-to-Valkey conversion rule that has no corresponding Valkey-to-Lua conversion rule:

There are three additional rules to note about converting Lua to Valkey data types:

  • Lua has a single numerical type, Lua numbers. There is no distinction between integers and floats. So we always convert Lua numbers into integer replies, removing the decimal part of the number, if any. If you want to return a Lua float, it should be returned as a string, exactly like Valkey itself does (see, for instance, the ZSCORE command).
  • There's no simple way to have nils inside Lua arrays due to Lua's table semantics. Therefore, when Valkey converts a Lua array to RESP, the conversion stops when it encounters a Lua nil value.
  • When a Lua table is an associative array that contains keys and their respective values, the converted Valkey reply will not include them.

Lua to RESP2 type conversion examples:

127.0.0.1:6379> EVAL "return 10" 0
(integer) 10

127.0.0.1:6379> EVAL "return { 1, 2, { 3, 'Hello World!' } }" 0
1) (integer) 1
2) (integer) 2
3) 1) (integer) 3
   1) "Hello World!"

127.0.0.1:6379> EVAL "return server.call('get','foo')" 0
"bar"

The last example demonstrates receiving and returning the exact return value of server.call() (or server.pcall()) in Lua as it would be returned if the command had been called directly.

The following example shows how floats and arrays that cont nils and keys are handled:

127.0.0.1:6379> EVAL "return { 1, 2, 3.3333, somekey = 'somevalue', 'foo', nil , 'bar' }" 0
1) (integer) 1
2) (integer) 2
3) (integer) 3
4) "foo"

As you can see, the float value of 3.333 gets converted to an integer 3, the somekey key and its value are omitted, and the string "bar" isn't returned as there is a nil value that precedes it.

RESP3 to Lua type conversion

RESP3 is a newer version of the protocol used by Valkey. It is available as an opt-in choice.

An executing script may call the server.setresp function during its execution and switch the protocol version that's used for returning replies from Valkey's commands (that can be invoked via server.call() or server.pcall()).

Once Valkey's replies are in RESP3 protocol, all of the RESP2 to Lua conversion rules apply, with the following additions:

  • Map reply -> Lua table with a single map field containing a Lua table representing the fields and values of the map.
  • Set reply -> Lua table with a single set field containing a Lua table representing the elements of the set as fields, each with the Lua Boolean value of true.
  • Null -> Lua nil.
  • True reply -> Lua true boolean value.
  • False reply -> Lua false boolean value.
  • Double reply -> Lua table with a single double field containing a Lua number representing the double value.
  • Big number reply -> Lua table with a single big_number field containing a Lua string representing the big number value (since Redis OSS 7.0).
  • Verbatim string reply -> Lua table with a single verbatim_string field containing a Lua table with two fields, string and format, representing the verbatim string and its format, respectively (since Redis OSS 7.0).

Lua to RESP3 type conversion

Regardless of the script's choice of protocol version set for replies with the [server.setresp() function] when it calls server.call() or server.pcall(), the user may opt-in to using RESP3 (with the HELLO 3 command) for the connection. Although the default protocol for incoming client connections is RESP2, the script should honor the user's preference and return adequately-typed RESP3 replies, so the following rules apply on top of those specified in the Lua to RESP2 type conversion section when that is the case.

  • Lua Boolean -> RESP3 Boolean reply (note that this is a change compared to the RESP2, in which returning a Boolean Lua true returned the number 1 to the Valkey client, and returning a false used to return a null.
  • Lua table with a single map field set to an associative Lua table -> RESP3 map reply.
  • Lua table with a single set field set to an associative Lua table -> RESP3 set reply. Values can be set to anything and are discarded anyway.
  • Lua table with a single double field to an associative Lua table -> RESP3 double reply.
  • Lua nil -> RESP3 null.

However, if the connection is set use the RESP2 protocol, and even if the script replies with RESP3-typed responses, Valkey will automatically perform a RESP3 to RESP2 conversion of the reply as is the case for regular commands. That means, for example, that returning the RESP3 map type to a RESP2 connection will result in the reply being converted to a flat RESP2 array that consists of alternating field names and their values, rather than a RESP3 map.

Additional notes about scripting

Using SELECT inside scripts

You can call the SELECT command from your Lua scripts, like you can with any normal client connection. The database selected by the Lua script only affects the execution context of the script, and does not modify the database that's selected by the client calling the script.

Runtime libraries

The Valkey Lua runtime context always comes with several pre-imported libraries.

The following standard Lua libraries are available to use:

In addition, the following external libraries are loaded and accessible to scripts:

os library

  • Since version: 8.0.0
  • Available in scripts: yes
  • Available in functions: yes

os provides a set of functions for dealing with date, time, and system commands. More details can be found in the Operating System Facilities. Note that for sandbox security, currently only the following os functions is exposed:

  • os.clock()

struct library

  • Available in scripts: yes
  • Available in functions: yes

struct is a library for packing and unpacking C-like structures in Lua. It provides the following functions:

All of struct's functions expect their first argument to be a format string.

struct formats

The following are valid format strings for struct's functions:

  • >: big endian
  • <: little endian
  • ![num]: alignment
  • x: padding
  • b/B: signed/unsigned byte
  • h/H: signed/unsigned short
  • l/L: signed/unsigned long
  • T: size_t
  • i/In: signed/unsigned integer with size n (defaults to the size of int)
  • cn: sequence of n chars (from/to a string); when packing, n == 0 means the whole string; when unpacking, n == 0 means use the previously read number as the string's length.
  • s: zero-terminated string
  • f: float
  • d: double
  • (space): ignored

struct.pack(x)

This function returns a struct-encoded string from values. It accepts a struct format string as its first argument, followed by the values that are to be encoded.

Usage example:

127.0.0.1:6379> EVAL "return struct.pack('HH', 1, 2)" 0
"\x01\x00\x02\x00"

struct.unpack(x)

This function returns the decoded values from a struct. It accepts a struct format string as its first argument, followed by encoded struct's string.

Usage example:

127.0.0.1:6379> EVAL "return { struct.unpack('HH', ARGV[1]) }" 0 "\x01\x00\x02\x00"
1) (integer) 1
2) (integer) 2
3) (integer) 5

struct.size(x)

This function returns the size, in bytes, of a struct. It accepts a struct format string as its only argument.

Usage example:

127.0.0.1:6379> EVAL "return struct.size('HH')" 0
(integer) 4

cjson library

  • Available in scripts: yes
  • Available in functions: yes

The cjson library provides fast JSON encoding and decoding from Lua. It provides these functions.

cjson.encode(x)

This function returns a JSON-encoded string for the Lua data type provided as its argument.

Usage example:

127.0.0.1:6379> EVAL "return cjson.encode({ ['foo'] = 'bar' })" 0
"{\"foo\":\"bar\"}"

cjson.decode(x)

This function returns a Lua data type from the JSON-encoded string provided as its argument.

Usage example:

127.0.0.1:6379> EVAL "return cjson.decode(ARGV[1])['foo']" 0 '{"foo":"bar"}'
"bar"

cmsgpack library

  • Available in scripts: yes
  • Available in functions: yes

The cmsgpack library provides fast MessagePack encoding and decoding from Lua. It provides these functions.

cmsgpack.pack(x)

This function returns the packed string encoding of the Lua data type it is given as an argument.

Usage example:

127.0.0.1:6379> EVAL "return cmsgpack.pack({'foo', 'bar', 'baz'})" 0
"\x93\xa3foo\xa3bar\xa3baz"

cmsgpack.unpack(x)

This function returns the unpacked values from decoding its input string argument.

Usage example:

127.0.0.1:6379> EVAL "return cmsgpack.unpack(ARGV[1])" 0 "\x93\xa3foo\xa3bar\xa3baz"
1) "foo"
2) "bar"
3) "baz"

bit library

  • Available in scripts: yes
  • Available in functions: yes

The bit library provides bitwise operations on numbers. Its documentation resides at Lua BitOp documentation It provides the following functions.

bit.tobit(x)

Normalizes a number to the numeric range for bit operations and returns it.

Usage example:

127.0.0.1:6379> EVAL 'return bit.tobit(1)' 0
(integer) 1

bit.tohex(x [,n])

Converts its first argument to a hex string. The number of hex digits is given by the absolute value of the optional second argument.

Usage example:

127.0.0.1:6379> EVAL 'return bit.tohex(422342)' 0
"000671c6"

bit.bnot(x)

Returns the bitwise not of its argument.

bit.bnot(x) bit.bor(x1 [,x2...]), bit.band(x1 [,x2...]) and bit.bxor(x1 [,x2...])

Returns either the bitwise or, bitwise and, or bitwise xor of all of its arguments. Note that more than two arguments are allowed.

Usage example:

127.0.0.1:6379> EVAL 'return bit.bor(1,2,4,8,16,32,64,128)' 0
(integer) 255

bit.lshift(x, n), bit.rshift(x, n) and bit.arshift(x, n)

Returns either the bitwise logical left-shift, bitwise logical right-shift, or bitwise arithmetic right-shift of its first argument by the number of bits given by the second argument.

bit.rol(x, n) and bit.ror(x, n)

Returns either the bitwise left rotation, or bitwise right rotation of its first argument by the number of bits given by the second argument. Bits shifted out on one side are shifted back in on the other side.

bit.bswap(x)

Swaps the bytes of its argument and returns it. This can be used to convert little-endian 32-bit numbers to big-endian 32-bit numbers and vice versa.

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