ARSET - Upstash Documentation

Use ARSET to write one or more values into an array, starting at a given index.

The first value goes to <index>, the next to <index> + 1, and so on, so a batch of readings can be placed at a known offset in one call. Any slot in the range that was empty becomes occupied, and any slot that already held a value is overwritten. The reply counts only the slots that were newly occupied, which makes it a cheap way to tell how much of a write was new data rather than a correction.

Writing past the end of the array does not shift anything: an array is sparse, so the slots between the previous highest index and the new one simply stay empty. ARSET never moves the append cursor used by ARINSERT, so mixing positional writes with appends is safe.

See the array command overview for the data model these commands share.

Syntax#

ARSET <key> <index> <value> [<value> ...]

Arguments#

Argument	Required	Repeatable	Description
`<key>`	Yes	No	Array key targeted by the command.
`<index>`	Yes	No	Zero-based index of the first value. Must be between `0` and `18446744073709551614`.
`<value>`	Yes	Yes	Value to store. Repeat to fill consecutive indexes starting at `<index>`.

Important points#

The reply counts newly occupied slots only. Overwriting an existing value contributes 0.
An index outside the supported range, or a batch whose last index would exceed it, returns ERR invalid array index.

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	Integer
RESP3	Integer

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

ARSET my-array 0 hello world

@upstash/redis

Note

This command is not supported yet in @upstash/redis.

upstash_redis

Note

This command is not supported yet in upstash_redis.

ioredis

import Redis from "ioredis";const redis = new Redis(process.env.REDIS_URL!);const result = await redis.arset("my-array", 0, "hello", "world");console.log(result);

node-redis

import { createClient } from "redis";const client = await createClient({ url: process.env.REDIS_URL })  .on("error", console.error)  .connect();const result = await client.arSet("my-array", 0, ["hello", "world"]);console.log(result);

redis-py

import osimport redisclient = redis.from_url(os.environ["REDIS_URL"])result = client.arset("my-array", 0, "hello", "world")print(result)

go-redis

package mainimport (    "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.ARSet(context.Background(), "my-array", 0, "hello", "world").Result()    if err != nil {        panic(err)    }    fmt.Println(result)}

jedis

import java.net.URI;import redis.clients.jedis.Jedis;try (Jedis jedis = new Jedis(new URI(System.getenv("REDIS_URL")))) {  Object result = jedis.arset("my-array", 0, "hello", "world");  System.out.println(result);}

redis-rs

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("ARSET");    command.arg("my-array");    command.arg("0");    command.arg("hello");    command.arg("world");    let result: redis::Value = command.query(&mut connection)?;    println!("{result:?}");    Ok(())}