Node Line Reader

Node Line Reader is a Node.js module that helps you reading lines of text from a file.

Features:

• Reads lines of text from Readable streams e.g. a file
• Reads lines that match one or more patterns
• Skips lines that match one or more patterns e.g. empty lines
• Reads part of a file

Installation:

npm install node-line-reader

Usage:

Using LineReader

1var path = require('path');
2var LineReader = require('node-line-reader').LineReader;
3
4var reader = new LineReader(path.join('/home/user', 'some-file.txt'));
5
6// Each execution of nextLine will get a following line of text from the input file
7reader.nextLine(function (err, line) {
8    if (!err) {
9        console.log('file line: ', line);
10    }
11});

Using LineTransform

1var stream = getSomeReadableStream(); // Create read stream
2var LineTransform = require('node-line-reader').LineTransform;  // LineTransform constructor
3var transform = new LineTransform();
4
5stream.pipe(transform); // Pipe input from a file stream over to line transform
6
7transform.on('data', function(line) {
8    // line - single line of text from input file
9});
10
11transform.on('end', function() {
12    // no more text lines
13});

Using LineFilter

1var stream = getSomeReadableStream(); // Create read stream
2var LineTransform = require('node-line-reader').LineTransform;  // LineTransform constructor
3var LineFilter = require('node-line-reader').LineFilter;  // LineFilter constructor
4
5var transform = new LineTransform();
6
7// Skip empty lines and lines with "et" (with leading and trailing space) in them
8var filter = new LineFilter({ skipEmpty: true, exclude: [/\bet\b/ });
9
10// Pipe input from a file stream over to line transform and to the filter
11stream.pipe(transform).pipe(filter); 
12
13filter.on('data', function(line) {
14    // line - single line of text from input file
15});
16
17filter.on('end', function() {
18    // no more text lines
19});

API:

Class: LineReader

LineReader is a text lines reader from a specified file.

'LineReader.nextLine(cb)'

This function reads another line of text from a specified file and passes it over to the callback method.

The callback has arguments (err, line). The err argument is an error that occurred while reading a line of text (null if no error occurred). The line is a string with line of text from a specified input file.

Class: LineFilter

LineFilter is a duplex stream passing through lines of text matching include and exclude rules. LineFilter instance can be piped into antoher Writable instance.

The LineFilter accepts options objects with following parameters:

• skipEmpty - boolean value blocking empty lines
• skipBlank - boolean value blocking blank lines (lines composed of whitespace characters)
• include - a single instance or an array of regular expressions (see below for text filtering rules)
• exclude - a single instance or an array of regular expressions (see below for text filtering rules)

Text filtering rules:

• If only include pattern(s) are provided, filter will pass through lines of text which are matched by the include pattern(s) only
• If only exclude pattern(s) are provided, fillter will pass through all lines except the ones which are matched by the exclude pattern(s) only
• If include and exclude pattern(s) are provided, filter filter will pass through lines of text which are matched by the include pattern(s) and not matched by the exclude pattern(s)

Event: 'readable'

When a line of text can be read from the transform, it will emit a 'readable' event.

Event: 'data'

• line Buffer | String The line of text.

Event: 'end'

This event fires when there will be no more test to read.

Event: 'close'

As Stream 'close' event: Emitted when the underlying resource (for example, the backing file descriptor) has been closed. Not all streams will emit this.

Event: 'error'

As Stream 'close' event: Emitted if there was an error receiving data.

Class: LineTransform

LineTransform is a duplex stream converting input text into lines of text. LineTransform instance can be piped into antoher Writable instance.

Event: 'readable'

When a line of text can be read from the transform, it will emit a 'readable' event.

Event: 'data'

• line Buffer | String The line of text.

Event: 'end'

This event fires when there will be no more test to read.

Event: 'close'

As Stream 'close' event: Emitted when the underlying resource (for example, the backing file descriptor) has been closed. Not all streams will emit this.

Event: 'error'

As Stream 'close' event: Emitted if there was an error receiving data.

Author

Writen by Tom Pawlak - Blog

License:

The MIT License (MIT)

Copyright © 2014 Tom Pawlak