re2

What is re2?

The re2 npm package is a wrapper around Google's RE2 regular expression library, which is designed to be fast and safe. It provides a way to perform regular expression operations without the risk of catastrophic backtracking, which can occur with some other regular expression engines.

What are re2's main functionalities?

Basic Matching

This feature allows you to perform basic matching operations using regular expressions. The code sample demonstrates how to create a new RE2 instance with a pattern and test a string against it.

const RE2 = require('re2');
const re = new RE2('hello');
console.log(re.test('hello world')); // true

Capturing Groups

This feature allows you to use capturing groups in your regular expressions. The code sample shows how to capture groups of digits separated by a hyphen and access the captured groups.

const RE2 = require('re2');
const re = new RE2('(\d+)-(\d+)');
const match = re.exec('123-456');
console.log(match[1]); // 123
console.log(match[2]); // 456

Global Matching

This feature allows you to perform global matching to find all occurrences of a pattern in a string. The code sample demonstrates how to find all sequences of digits in a string.

const RE2 = require('re2');
const re = new RE2('\d+', 'g');
const matches = '123 456 789'.match(re);
console.log(matches); // ['123', '456', '789']

Replacing

This feature allows you to replace parts of a string that match a pattern with a replacement string. The code sample shows how to replace 'world' with 'RE2' in a given string.

const RE2 = require('re2');
const re = new RE2('world');
const result = 'hello world'.replace(re, 'RE2');
console.log(result); // 'hello RE2'

Other packages similar to re2

regexp

The 'regexp' package provides a simple interface for working with regular expressions in JavaScript. It is similar to re2 but does not offer the same level of performance and safety guarantees against catastrophic backtracking.

xregexp

The 'xregexp' package extends JavaScript's native RegExp with additional features and syntax. It offers more functionality than re2 but may not be as performant or safe in terms of avoiding catastrophic backtracking.

pcre-to-regexp

The 'pcre-to-regexp' package allows you to convert Perl-compatible regular expressions (PCRE) to JavaScript RegExp objects. While it provides compatibility with PCRE syntax, it does not offer the same performance and safety benefits as re2.

README

node-re2

This project provides bindings for RE2: fast, safe alternative to backtracking regular expression engines written by Russ Cox. To learn more about RE2, start with an overview Regular Expression Matching in the Wild. More resources can be found at his Implementing Regular Expressions page.

RE2's regular expression language is almost a superset of what is provided by RegExp (see Syntax), but it lacks one feature: backreferences. See below for more details.

RE2 object emulates standard RegExp making it a practical drop-in replacement in most cases. RE2 is extended to provide String-based regular expression methods as well. To help converting RegExp objects to RE2 its constructor can take RegExp directly honoring all properties.

It can work with node.js buffers directly reducing overhead on recoding and copying characters, and making processing/parsing long files fast.

Standard features

RE2 object can be created just like RegExp:

• new RE2(pattern[, flags])

Supported properties:

• re2.lastIndex
• re2.global
• re2.ignoreCase
• re2.multiline
• re2.source

Supported methods:

• re2.exec(str)
• re2.test(str)
• re2.toString()

Extensions

Shortcut construction

RE2 object can be created from a regular expression:

var re1 = new RE2(/ab*/ig); // from a RegExp object
var re2 = new RE2(re1);     // from another RE2 object

String methods

Standard String defines four more methods that can use regular expressions. RE2 provides them as methods exchanging positions of a string, and a regular expression:

• re2.match(str)
  • See str.match(regexp)
• re2.replace(str, newSubStr|function)
  • See str.replace(regexp, newSubStr|function)
• re2.search(str)
  • See str.search(regexp)
• re2.split(str[, limit])
  • See str.split(regexp[, limit])

Buffer support

In order to support Buffer directly, most methods can accept buffers instead of strings. It speeds up all operations. Following signatures are supported:

• re2.exec(buf)
• re2.test(buf)
• re2.match(buf)
• re2.search(buf)
• re2.split(buf[, limit])
• re2.replace(buf, replacer)

Differences with their string-based versions:

• All buffers are assumed to be encoded as UTF-8 (ASCII is a proper subset of UTF-8).
• Instead of strings they return Buffer objects, even in composite objects. A buffer can be converted to a string with buf.toString().
• All offsets and lengths are in bytes, rather than characters (each UTF-8 character can occupy from 1 to 4 bytes). This way users can properly slice buffers without costly recalculations from characters to bytes.

When re2.replace() is used with a replacer function, the replacer can return a buffer, or a string. But all arguments (except for an input object) will be strings, and an offset will be in characters. If you prefer to deal with buffers and byte offsets in a replacer function, set a property useBuffers to true on the function:

function strReplacer(match, offset, input) {
	// typeof match == "string"
	return "<= " + offset + " characters|";
}

RE2("б").replace("абв", strReplacer);
// "а<= 1 characters|в"

function bufReplacer(match, offset, input) {
	// typeof match == "string"
	return "<= " + offset + " bytes|";
}
bufReplacer.useBuffers = true;

RE2("б").replace("абв", bufReplacer);
// "а<= 2 bytes|в"

This feature works for string and buffer inputs. If a buffer was used as an input, its output will be returned as a buffer too, otherwise a string will be returned.

Calculate length

Two functions to calculate string sizes between UTF-8 and UTF-16 are exposed on RE2:

• RE2.getUtf8Length(str) — calculates a buffer size in bytes to encode a UTF-16 string as a UTF-8 buffer.
• RE2.getUtf16Length(buf) — calculates a string size in characters to encode a UTF-8 buffer as a UTF-16 string.

JavaScript supports UCS-2 strings with 16-bit characters, while node.js 0.11 supports full UTF-16 as a default string.

How to install

Installation:

npm install re2

How to use

It is used just like a RegExp object.

var RE2 = require("re2");

// with default flags
var re = new RE2("a(b*)");
var result = re.exec("abbc");
console.log(result[0]); // "abb"
console.log(result[1]); // "bb"

result = re.exec("aBbC");
console.log(result[0]); // "a"
console.log(result[1]); // ""

// with explicit flags
re = new RE2("a(b*)", "i");
result = re.exec("aBbC");
console.log(result[0]); // "aBb"
console.log(result[1]); // "Bb"

// from regular expression object
var regexp = new RegExp("a(b*)", "i");
re = new RE2(regexp);
result = re.exec("aBbC");
console.log(result[0]); // "aBb"
console.log(result[1]); // "Bb"

// from regular expression literal
re = new RE2(/a(b*)/i);
result = re.exec("aBbC");
console.log(result[0]); // "aBb"
console.log(result[1]); // "Bb"

// from another RE2 object
var rex = new RE2(re);
result = rex.exec("aBbC");
console.log(result[0]); // "aBb"
console.log(result[1]); // "Bb"

// shortcut
result = new RE2("ab*").exec("abba");

// factory
result = RE2("ab*").exec("abba");

Backreferences

Unlike RegExp, RE2 doesn't support backreferences, which are numbered references to previously matched groups, like so: \1, \2, and so on. Example of backrefrences:

/(cat|dog)\1/.test("catcat"); // true
/(cat|dog)\1/.test("dogdog"); // true
/(cat|dog)\1/.test("catdog"); // false
/(cat|dog)\1/.test("dogcat"); // false

If your application uses this kind of matching, you should continue to use RegExp.

Release history

• 1.2.0 Documented getUtfXLength() functions. Added support for \c and \u commands.
• 1.1.1 Minor corrections in README.
• 1.1.0 Buffer-based API is public. Unicode is fully supported.
• 1.0.0 implemeted all RegExp methods, and all relevant String methods
• 0.9.0 the initial public release