tail v2.2.6
Tail
The zero dependency Node.js module for tailing a file
Made with ❤️ by Luca Grulla
- 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). Passnull
for is binary files with no line separator.fsWatchOptions
: the full set of options that can be passed tofs.watch
as per node documentation (default: {}).fromBeginning
: tail from the beginning of the file (default:false
). IffromBeginning
is truenLines
will be ignored.follow
: simulatetail -F
option. In the case the file is moved/renamed/logrotated, if set totrue
will start tailing again after a 1 second delay; if set tofalse
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 iffromBeginning
is set totrue
.useWatchFile
: if set totrue
will force the use offs.watchFile
over delegating to the library the choice betweenfs.watch
andfs.watchFile
(default:false
).encoding
: the file encoding (default:utf-8
).flushAtEOF
: set totrue
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.
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