tail

Tail

The zero dependency Node.js module for tailing a file

Author: Luca Grulla - www.lucagrulla.com

Installation

npm install tail

Use

Tail = require('tail').Tail;

tail = new Tail("fileToTail");

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

tail.on("error", function(error) {
  console.log('ERROR: ', error);
});

If you want to stop tail:

tail.unwatch()

To start watching again:

tail.watch()

Configuration

The only mandatory parameter is the path to the file to tail.

var fileToTail = "/path/to/fileToTail.txt";
new Tail(fileToTail)

If the file is missing or invalid Tail constructor will throw an Exception and won't initialize.

try {
  new Tail('missingFile.txt')
} catch ex {
  console.log(ex)
}

Optional parameters can be passed via a hash:

var options= {separator: /[\r]{0,1}\n/, fromBeginning: false, fsWatchOptions: {}, follow: true, logger: console}
new Tail(fileToTail, options)

Constructor parameters

• separator: the line separator token (default: /[\r]{0,1}\n/ to handle linux/mac (9+)/windows). Pass null if your file is binary there's no line separator.
• fsWatchOptions: the full set of options that can be passed to fs.watch as per node documentation (default: {}).
• fromBeginning: forces the tail of the file from the very beginning of it instead of from the first new line that will be appended (default: false).
• follow: simulate tail -F option. In the case the file is moved/renamed (or logrotated), if set to true tail will try to start tailing again after a 1 second delay, if set to false it will just emit an error event (default: true).
• logger: a logger object(default: no logger). The passed logger has to respond to two methods:
  • info([data][, ...])
  • error([data][, ...])
• useWatchFile: if set to true will force the use of fs.watchFile rather than delegating to the library the choice between fs.watch and fs.watchFile (default: false).
• encoding: the encoding of the file to tail (default:utf-8).
• flushAtEOF: set to true if you want to force flush of content when end of file is reached. Particularly useful when there's no separator character at the end of the file (default: false).

Emitted events

Tail emits two events:

• line

tail.on('line', (data) => {
  console.log(data)  
})

• error

tail.on('error', (err) => {
  console.log(err)  
})

How to contribute

Tail is written in plain ES6.Pull Requests are welcome.

History

Tail was born as part of a data firehose. Read about it here. Tail original version was written in CoffeeScript. Since 2020 it's pure ES6.

License

MIT. Please see License file for more details.