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tail
DefinitelyTyped icon, indicating that this package has TypeScript declarations provided by the separate @types/tail package

2.2.0 • Public • Published

Tail

The zero dependency Node.js module for tailing a file

NPM

license npm npm

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 for is binary files with no line separator.
  • fsWatchOptions: the full set of options that can be passed to fs.watch as per node documentation (default: {}).
  • fromBeginning: tail from the beginning of the file (default: false). If fromBeginning is true nLines will be ignored.
  • follow: simulate tail -F option. In the case the file is moved/renamed/logrotated, if set to true will start tailing again after a 1 second delay; if set to false it will emit an error event (default: true).
  • logger: a logger object(default: no logger). The passed logger should follow the folliwing signature:
    • info([data][, ...])
    • error([data][, ...])
  • nLines: tail from the last n lines. (default: undefined). Ignored if fromBeginning is set to true.
  • useWatchFile: if set to true will force the use of fs.watchFile over delegating to the library the choice between fs.watch and fs.watchFile (default: false).
  • encoding: the file encoding (default:utf-8).
  • flushAtEOF: set to true to force flush of content when end of file is reached. 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 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 December 2020 it's pure ES6.

License

MIT. Please see License file for more details.

Keywords

Install

npm i tail

DownloadsWeekly Downloads

204,591

Version

2.2.0

License

MIT

Unpacked Size

13.7 kB

Total Files

5

Last publish

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