How to do `tail -f logfile.txt`-like processing in node.js?

Question

tail -f logfile.txt outputs the last 10 lines of logfile.txt, and then continues to output appended data as the file grows.

What's the recommended way of doing the -f part in node.js?

The following outputs the entire file (ignoring the "show the last 10 lines") and then exits.

var fs = require('fs');
var rs = fs.createReadStream('logfile.txt', { flags: 'r', encoding: 'utf8'});
rs.on('data', function(data) {
  console.log(data);
});

I understand the event-loop is exiting because after the stream end & close event there are no more events -- I'm curious about the best way of continuing to monitor the stream.

question from:https://stackoverflow.com/questions/8993611/how-to-do-tail-f-logfile-txt-like-processing-in-node-js

Answer 1

The canonical way to do this is with fs.watchFile.

Alternatively, you could just use the node-tail module, which uses fs.watchFile internally and has already done the work for you. Here is an example of using it straight from the documentation:

Tail = require('tail').Tail;

tail = new Tail("fileToTail");

tail.on("line", function(data) {
  console.log(data);
});