docs/functions-deploy-trigger.md

---
id: functions-deploy-trigger
title: Trigger a function
sidebar_label: "Trigger a function"
description: Learn to trigger a function in Pulsar.
---

Triggering a function means that you invoke a function by producing a message to one of the input topics via the CLI. You can use the `trigger` command to trigger a function at any time.

:::tip

With the [`pulsar-admin`](pathname:///reference/#/@pulsar:version_reference@/pulsar-admin/) CLI, you can send messages to functions without using the [`pulsar-client`](reference-cli-tools.md) tool or a language-specific client library.

:::

To learn how to trigger a function, you can start with a Python function that returns a simple string based on the input as follows.

```python
# myfunc.py
def process(input):
    return "This function has been triggered with a value of {0}".format(input)
```

1. Run the function in cluster mode.

  ```bash
  bin/pulsar-admin functions create \
    --tenant public \
    --namespace default \
    --name myfunc \
    --py myfunc.py \
    --classname myfunc \
    --inputs persistent://public/default/in \
    --output persistent://public/default/out
  ```

2. Assign a consumer to listen on the output topic for messages from the `myfunc` function with the [`pulsar-client consume`](reference-cli-tools.md) command.

  ```bash
  bin/pulsar-client consume persistent://public/default/out \
    --subscription-name my-subscription \
    --num-messages 0 # Listen indefinitely
  ```

3. Trigger the function.

   ```bash
   bin/pulsar-admin functions trigger \
     --tenant public \
     --namespace default \
     --name myfunc \
     --trigger-value "hello world"
   ```

   :::tip

   In the `trigger` command, topic info is not required. You only need to specify basic information about the function, such as tenant, namespace, and function name.

   :::

The consumer listening on the output topic produces something as follows in the log.

```text
----- got message -----
This function has been triggered with a value of hello world
```