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RE2 is a software library which implements a regular expression engine. It uses finite-state machines, in contrast to most other regular expression libraries. RE2 supports a C++ interface. RE2 was implemented by Google and Google uses RE2 for Google products. [3]
Regular Expression Flavor Comparison – Detailed comparison of the most popular regular expression flavors; Regexp Syntax Summary; Online Regular Expression Testing – with support for Java, JavaScript, .Net, PHP, Python and Ruby; Implementing Regular Expressions – series of articles by Russ Cox, author of RE2; Regular Expression Engines
The algorithm works recursively by splitting an expression into its constituent subexpressions, from which the NFA will be constructed using a set of rules. [3] More precisely, from a regular expression E, the obtained automaton A with the transition function Δ [clarification needed] respects the following properties:
Regular expressions are used in search engines, in search and replace dialogs of word processors and text editors, in text processing utilities such as sed and AWK, and in lexical analysis. Regular expressions are supported in many programming languages. Library implementations are often called an "engine", [4] [5] and many of these are ...
Unlike keyword searching, regex searching is by default case-sensitive, does not ignore punctuation, and operates directly on the page source (MediaWiki markup) rather than on the rendered contents of the page. To perform a regex search, use the ordinary search box with the syntax insource:/regex/ or intitle:/regex/.
Perl Compatible Regular Expressions (PCRE) is a library written in C, which implements a regular expression engine, inspired by the capabilities of the Perl programming language. Philip Hazel started writing PCRE in summer 1997. [ 3 ]
This example uses some of the following regular expression metacharacters (sed supports the full range of regular expressions): The caret (^) matches the beginning of the line. The dollar sign ($) matches the end of the line. The asterisk (*) matches zero or more occurrences of the previous character.
Oniguruma (鬼車) is a free and open-source regular expression library that supports a variety of character encodings, written by K. Kosako.The Ruby programming language, in version 1.9, as well as PHP's multi-byte string module (since PHP5), use Oniguruma as their regular expression engine. [2]