123 lines
3.6 KiB
Markdown
123 lines
3.6 KiB
Markdown
# Tail
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The **zero** dependency Node.js module for tailing a file
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[](https://nodei.co/npm/tail.png?downloads=true&downloadRank=true)
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[](https://github.com/lucagrulla/node-tail/blob/master/LICENSE)
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[](https://www.npmjs.com/package/tail)
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Made with ❤️ by [Luca Grulla](https://www.lucagrulla.com)
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1. TOC
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{:toc}
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## Installation
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```bash
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npm install tail
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```
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## Use
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```javascript
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Tail = require('tail').Tail;
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tail = new Tail("fileToTail");
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tail.on("line", function(data) {
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console.log(data);
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});
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tail.on("error", function(error) {
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console.log('ERROR: ', error);
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});
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```
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If you want to stop tail:
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```javascript
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tail.unwatch()
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```
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To start watching again:
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```javascript
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tail.watch()
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```
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## Configuration
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The only mandatory parameter is the path to the file to tail.
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```javascript
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var fileToTail = "/path/to/fileToTail.txt";
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new Tail(fileToTail)
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```
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If the file is **missing or invalid** ```Tail``` constructor will throw an Exception and won't initialize.
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```javascript
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try {
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new Tail('missingFile.txt')
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} catch (ex) {
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console.log(ex)
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}
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```
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Optional parameters can be passed via a hash:
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```javascript
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var options= {separator: /[\r]{0,1}\n/, fromBeginning: false, fsWatchOptions: {}, follow: true, logger: console}
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new Tail(fileToTail, options)
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```
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### Constructor parameters
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* `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.
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* `fsWatchOptions`: the full set of options that can be passed to `fs.watch` as per node documentation (default: {}).
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* `fromBeginning`: tail from the beginning of the file (default: `false`). If `fromBeginning` is true `nLines` will be ignored.
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* `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`).
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* `logger`: a logger object(default: no logger). The passed logger should follow the folliwing signature:
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* `info([data][, ...])`
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* `error([data][, ...])`
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* `nLines`: tail from the last n lines. (default: `undefined`). Ignored if `fromBeginning` is set to `true`.
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* `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`).
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* `encoding`: the file encoding (default:`utf-8`).
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* `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`).
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## Emitted events
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`Tail` emits two events:
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* line
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```javascript
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tail.on('line', (data) => {
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console.log(data)
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})
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```
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* error
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```javascript
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tail.on('error', (err) => {
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console.log(err)
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})
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```
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The error emitted is either the underline exception or a descriptive string.
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## How to contribute
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Node Tail code repo is [here](https://github.com/lucagrulla/node-tail/)
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Tail is written in ES6. Pull Requests are welcome.
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## History
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Tail was born as part of a data firehose. Read more about that project [here](https://www.lucagrulla.com/posts/building-a-firehose-with-nodejs/).
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Tail originally was written in [CoffeeScript](https://coffeescript.org/). Since December 2020 it's pure ES6.
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## License
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MIT. Please see [License](https://github.com/lucagrulla/node-tail/blob/master/LICENSE) file for more details.
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