docs/functions-deploy-trigger.md

id: functions-deploy-trigger title: Trigger a function sidebar_label: “Trigger a function”

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 CLI, you can send messages to functions without using the pulsar-client 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.

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

Run the function in cluster mode.

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

Assign a consumer to listen on the output topic for messages from the myfunc function with the pulsar-client consume command.

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

Trigger the function.
```
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.

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