# EVALSHA_RO

> Run a cached script that does not write.

Use `EVALSHA_RO` to run a script cached by its SHA1 digest. The script may not write to the database.

It is the read-only form of [`EVALSHA`](/redis/commands/scripting/evalsha): any write command called from the script fails, which lets the server run it on replicas. As with `EVALSHA`, a digest that is not in the cache produces a `NOSCRIPT` error, and the caller is expected to fall back to [`EVAL_RO`](/redis/commands/scripting/eval-ro) with the script body.

Read-only scripts take the global lock like any other script unless the cached body's shebang sets the `allow-key-locking` flag, for example `#!lua flags=no-writes,allow-key-locking`. With the flag, the call takes shared read locks on the keys passed in `KEYS`. See [Key-Based Locking](/redis/features/key-locking).

## Syntax

```redis
EVALSHA_RO <sha1> <numkeys> [<key> [<key> ...]] [<arg> [<arg> ...]]
```

## Arguments

| Argument | Required | Repeatable | Description |
| --- | --- | --- | --- |
| `<sha1>` | Yes | No | SHA1 digest of a script cached with `SCRIPT LOAD`. |
| `<numkeys>` | Yes | No | Number of key arguments that follow. |
| `<key>` | No | Yes | Redis key targeted by the command. |
| `<arg>` | No | Yes | Additional argument, available to the script as `ARGV`. |

## Important points

- `numkeys` must equal the number of key arguments that immediately follow it; remaining arguments are available to the script or function as ordinary arguments.
- A read-only script still takes the global lock unless the cached body's shebang sets the `allow-key-locking` flag. See [Key-Based Locking](/redis/features/key-locking).
- Pass every key the script reads through `KEYS` whether or not `allow-key-locking` is set. A key built inside the script is read from disk under the lock when it is not in memory, and it is rejected outright when the flag is set. See [Dynamic Keys and Latency](/redis/features/key-locking#dynamic-keys-and-latency).

## Reply conversion

`redis.setresp()` and the RESP2 and RESP3 conversions applied to `redis.call` replies work exactly as they do for [`EVAL`](/redis/commands/scripting/eval#reply-conversion).

## 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 | Reply produced by the cached read-only script |
| RESP3 | Reply produced by the cached read-only script |

<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
EVALSHA_RO fb67a0c03b48ddbf8b4c9b011e779563bdbc28cb 0 value
```

</Accordion>

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

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

const redis = Redis.fromEnv();

const result = await redis.evalshaRo("fb67a0c03b48ddbf8b4c9b011e779563bdbc28cb", [], ["hello"]);
console.log(result) // "hello"
```

</Accordion>

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

```python
from upstash_redis import Redis

redis = Redis.from_env()
result = redis.evalsha_ro("<sha1>", args=["value"])
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.evalsha_ro("<sha1>", "0", "value");
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.evalShaRo("<sha1>", { arguments: ["value"] });
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.evalsha_ro("<sha1>", 0, "value")
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.EvalShaRO(context.Background(), "<sha1>", nil, "value").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.evalshaReadonly("<sha1>", java.util.List.of(), java.util.List.of("value"));
  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("EVALSHA_RO");
    command.arg("<sha1>");
    command.arg("1");
    let result: redis::Value = command.query(&mut connection)?;
    println!("{result:?}");
    Ok(())
}
```

</Accordion>

</AccordionGroup>