file-write

Overview

The file-write node writes msg.payload to a file on the local filesystem. It supports write (overwrite) and append modes, automatic directory creation, configurable encoding, and optional newline appending. The filename can be set in the node configuration or dynamically via msg.filename.

Properties

Write Modes

Write 1: "Hello"    -> File: Hello
Write 2: "World"    -> File: World

Write 1: "Hello"    -> File: Hello
Write 2: "World"    -> File: Hello\nWorld

Example: Append Sensor Data to CSV Log

Continuously append temperature readings to a CSV file. Each sensor reading is formatted as a CSV line and appended with a newline.

// Function node to format CSV line:
const ts = new Date().toISOString();
const temp = msg.payload.temperature;
const hum = msg.payload.humidity;
const sensor = msg.payload.sensor_id;

msg.payload = ts + "," + sensor + "," + temp + "," + hum;
return msg;

// file-write node configuration:
{
  "filename": "/data/logs/sensor-readings.csv",
  "action": "append",
  "createDir": true,
  "encoding": "utf-8",
  "addNewline": true,
  "overwriteFile": false
}

// Resulting CSV file after multiple writes:
// 2024-01-15T10:00:00Z,dht22-01,23.5,65
// 2024-01-15T10:05:00Z,dht22-01,23.7,64
// 2024-01-15T10:10:00Z,dht22-01,23.4,66

Example: Write JSON Config File

Save updated configuration as a formatted JSON file. Overwrites the entire file each time to ensure the config is always consistent.

// Function node to prepare config:
const config = flow.get('config') || {};
config.lastUpdated = new Date().toISOString();
config.sensors = config.sensors || [];

// Pretty-print JSON for readability
msg.payload = JSON.stringify(config, null, 2);
return msg;

// file-write node configuration:
{
  "filename": "/etc/edgeflow/sensors.json",
  "action": "write",
  "createDir": true,
  "encoding": "utf-8",
  "addNewline": true,
  "overwriteFile": true
}

// Written file:
// {
//   "lastUpdated": "2024-01-15T14:30:00Z",
//   "sensors": [
//     { "id": "dht22-01", "pin": 4 },
//     { "id": "bme280-01", "bus": 1 }
//   ]
// }

Example: Dynamic Filename by Date

Create daily log files by dynamically setting the filename based on the current date.

// Function node to set dynamic filename:
const now = new Date();
const date = now.toISOString().split('T')[0]; // 2024-01-15
msg.filename = "/data/logs/" + date + "-readings.csv";
msg.payload = now.toISOString() + "," + msg.payload;
return msg;

// file-write node configuration:
{
  "filename": "",
  "action": "append",
  "createDir": true,
  "addNewline": true
}

// Creates files like:
// /data/logs/2024-01-14-readings.csv
// /data/logs/2024-01-15-readings.csv

Common Use Cases