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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
A regular expression (shortened as regex or regexp), [1] sometimes referred to as rational expression, [2] [3] is a sequence of characters that specifies a match pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings , or for input validation .
Regular languages are a category of languages (sometimes termed Chomsky Type 3) which can be matched by a state machine (more specifically, by a deterministic finite automaton or a nondeterministic finite automaton) constructed from a regular expression. In particular, a regular language can match constructs like "A follows B", "Either A or B ...
If the regex itself is affected by user input, such as a web service permitting clients to provide a search pattern, then an attacker can inject a malicious regex to consume the server's resources. Therefore, in most cases, regular expression denial of service can be avoided by removing the possibility for the user to execute arbitrary patterns ...
Different approximate matchers impose different constraints. Some matchers use a single global unweighted cost, that is, the total number of primitive operations necessary to convert the match to the pattern. For example, if the pattern is coil, foil differs by one substitution, coils by one insertion, oil by one deletion, and foal by two ...
Replaces matches of multiple patterns in a given string with given replacements. For each replacement instance, the pattern matching at the lowest position is chosen. If there are multiple such patterns, then the one specified earliest in the pattern list is chosen.
Commentz-Walter has two phases it must go through, these being a pre-computing phase and a matching phase. For the first phase, the Commentz-Walter algorithm uses a reversed pattern to build a pattern tree, this is considered the pre-computing phase. The second phase, known as the matching phase, takes into account the other two algorithms.
grep is a command-line utility for searching plaintext datasets for lines that match a regular expression.Its name comes from the ed command g/re/p (global regular expression search and print), which has the same effect.