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continuous file tail. robust enough to survive rollovers.


Node.js module for continuously tailing a file.

It differs from other tail modules in that it survives truncates, file rollovers (e.g. mv /var/log/test /var/log/test.1), and unlink.

It does this by monitoring the filename, and when the inode changes, it will continue to read to the end of the existing file descriptor, then automatically read from the newly created file with the same name.

It emits a 'line' event when a new line is read.

npm install always-tail

var Tail = require('always-tail');
var fs = require('fs');
var filename = "/tmp/testlog";
if (!fs.existsSync(filename)) fs.writeFileSync(filename, "");
var tail = new Tail(filename, '\n');
tail.on('line', function(data) {
  console.log("got line:", data);
tail.on('error', function(data) {
  console.log("error:", data);
// to unwatch and close all file descriptors, tail.unwatch(); 
var tail = new Tail(filename, separator, options); 

filename - filename to monitor

separator - optional separator for each line (default: \n)

options.interval - optional interval to check for changes

options.start - optional start byte to start reading from

options.blockSize - maximum reading block size (default is 1 MB)

Code is heavily modified from the node-tail module (