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Every regular expression can be written solely in terms of the Kleene star and set unions over finite words. This is a surprisingly difficult problem. As simple as the regular expressions are, there is no method to systematically rewrite them to some normal form. The lack of axiom in the past led to the star height problem.
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/.
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
In the case of a web application, the programmer may use the same regular expression to validate input on both the client and the server side of the system. An attacker could inspect the client code, looking for evil regular expressions, and send crafted input directly to the web server in order to hang it.
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]
For a cheat sheet on writing regexes, see Wikipedia:AutoWikiBrowser/Regular expression. For case insensitive searches, include an "i" after the closing forward slash. Searching with regex offline. To search all of Wikipedia offline using regex, you need to download the Wikipedia database and do the search offline with AutoWikiBrowser's Database ...
TRE is an open-source library for pattern matching in text, [2] which works like a regular expression engine with the ability to do approximate string matching. [3] It was developed by Ville Laurikari [1] and is distributed under a 2-clause BSD-like license.
Ragel's input is a regular expression only in the sense that it describes a regular language; it is usually not written in a concise regular expression, but written out into multiple parts like in Extended Backus–Naur form. For example, instead of supporting POSIX character classes in regex syntax, Ragel implements them as built-in production ...