Custom Trigger

The Custom Trigger runs an external command or script and uses its output to determine whether an event occurred. This allows you to integrate any monitoring logic that can be expressed as a command-line program.

Configuration

Option	Type	Description
Command	String	The shell command or script to execute. The previous state is provided in stdin buffer. The working directory is the Scripts Directory set in app settings.
Timeout (ms)	Integer	Maximum execution time in milliseconds.

Command Contract

The command receives the previous state (Base64-encoded) as an argument. It must output a JSON object on stdout with the following format:

{
  "data": "<base64-encoded UTF-8 event data>",
  "newState": "<base64-encoded UTF-8 new state>"
}

• data: The event payload if an event occurred. Leave empty if no event.
• newState: The new state to persist for the next execution.

If the command exits without printing anything (or prints invalid JSON), no event is emitted.

Example

A simple bash script that fires an event with data "Hello World #{num}" where num is the current count:

#!/usr/bin/env python3
"""
always.py - A custom trigger that always returns an event with "Hello World" data.
This script simulates a trigger that always finds an event.
"""

import json
import base64
import sys
import os

def main():
    # Read previous state from stdin (if any)
    prev_state = sys.stdin.read().strip()
    if len(prev_state) == 0:
        prev_state = "0"
    num = int(prev_state) + 1
    
    # Create sample data
    data_string = f"Hello World #{num}"
    
    # Encode data in base64 for JSON transport
    encoded_data = base64.b64encode(data_string.encode('utf-8')).decode('utf-8')
    encoded_new_state = base64.b64encode(str(num).encode('utf-8')).decode('utf-8')
    
    # Create result JSON
    result = {
        "data": encoded_data,
        "newState": encoded_new_state
    }
    
    # Output JSON to stdout
    print(json.dumps(result))
    
    # For debugging, write to stderr (will be captured in logs)
    print(f"Trigger executed. Previous state: '{prev_state}'", file=sys.stderr)

if __name__ == "__main__":
    main()

Return Values

Key	Value
data	The returned data from the command / script.
newState	The returned newState from the command / script