# HSCAN

> Incrementally iterate hash fields.

Use `HSCAN` to iterate the fields of a hash in batches instead of reading it all at once.

Each call takes a cursor and returns the next cursor together with a batch of field and value pairs. Start at cursor `0` and keep calling with the cursor from the previous reply until the server returns `0`, which ends the iteration. Because each call does a bounded amount of work, this avoids the long single reply that [`HGETALL`](/redis/commands/hash/hgetall) produces on a large hash.

`MATCH` filters field names with a glob-style pattern, `COUNT` hints at how much work each call should do, and `NOVALUES` returns field names only, which is noticeably cheaper when values are large and you do not need them. Filtering is applied after a batch has been read, so a call can return nothing while the cursor is still non-zero: only a cursor of `0` means the iteration is over. Fields present for the whole iteration are returned at least once, and fields added or removed while it runs may or may not appear.

## Syntax

```redis
HSCAN <key> <cursor> [MATCH <pattern>] [COUNT <count>] [NOVALUES]
```

## Arguments

| Argument | Required | Repeatable | Description |
| --- | --- | --- | --- |
| `<key>` | Yes | No | Redis key targeted by the command. |
| `<cursor>` | Yes | No | Cursor returned by the previous call; start at `0`. |
| `MATCH <pattern>` | No | No | Return only elements matching this glob-style pattern. |
| `COUNT <count>` | No | No | Hint for how much work each iteration should do. |
| `NOVALUES` | No | No | Return only field names, without their values. |

## Important points

- This operation can inspect a large part of the database. Prefer cursor-based scans where possible and avoid unbounded use on hot paths.
- The cursor is opaque. Start with `0` and continue until the server returns cursor `0`; a single iteration may return no elements.

## 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 | Two-element array: cursor and flat field/value array, or field array with `NOVALUES` |
| RESP3 | Two-element array: cursor and flat field/value array, or field array with `NOVALUES` |

<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
HSCAN my-key 0
```

</Accordion>

<Accordion title="@upstash/redis" icon="node-js" iconType="brands">

```ts
import { Redis } from "@upstash/redis";

const redis = Redis.fromEnv();

await redis.hset("key", {
  id: 1,
  username: "chronark",
  name: "andreas"
 });
const [newCursor, fields] = await redis.hscan("key", 0);
console.log(newCursor); // likely `0` since this is a very small hash
console.log(fields); // ["id", 1, "username", "chronark", "name", "andreas"]
```

</Accordion>

<Accordion title="upstash_redis" icon="python" iconType="brands">

```python
from upstash_redis import Redis

redis = Redis.from_env()
result = redis.hscan("my-key", 0)
print(result)
```

</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.hscan("my-key", "0");
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.hScan("my-key", "0");
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.hscan("my-key", 0)
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.HScan(context.Background(), "my-key", 0, "*", 0).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.hscan("my-key", "0");
  System.out.println(result);
}
```

</Accordion>

<Accordion title="redis-rs" icon="rust" iconType="brands">

```rust
use redis::TypedCommands;

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 iter: redis::Iter<(String, String)> = connection.hscan("my-key")?;
    for (field, value) in iter {
        println!("{field}: {value}");
    }
    Ok(())
}
```

</Accordion>

</AccordionGroup>