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

    2.2.3 • Public • Published

    Tail

    The zero dependency Node.js module for tailing a file

    NPM

    license npm npm

    Made with ❤️ by Luca Grulla

    1. TOC {:toc}

    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)  
    })

    The error emitted is either the underline exception or a descriptive string.

    How to contribute

    Node Tail code repo is here Tail is written in ES6. Pull Requests are welcome.

    History

    Tail was born as part of a data firehose. Read more about that project here. Tail originally 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

    199,166

    Version

    2.2.3

    License

    MIT

    Unpacked Size

    16.5 kB

    Total Files

    7

    Last publish

    Collaborators

    • lucagrulla