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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 .
* matches the preceding character or group any number of times (including zero). For example, insource:/ab*(cd)*/ is matched by a, abbb, acdcd, etc.? matches the preceding character or group exactly zero or one times. { } match the preceding character or group a fixed number of times.
Greed, in regular expression context, describes the number of characters which will be matched (often also stated as "consumed") by a variable length portion of a regular expression – a token or group followed by a quantifier, which specifies a number (or range of numbers) of tokens. If the portion of the regular expression is "greedy", it ...
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 ...
Replace the next match. This button first highlights the forward searched match and replaces it after the next button push. Case sensitive: Toggle the case sensitive search setting. This does not affect the type ahead which always finds case insensitive. RegExp: Toggle the regular expression search setting. The JavaScript regular expression ...
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.
When REGEXP matches the input string, control flow is transferred to the associated CODE. There is one special rule: the default rule with * instead of REGEXP ; it is triggered if no other rules matches. re2c has greedy matching semantics: if multiple rules match, the rule that matches longer prefix is preferred; if the conflicting rules match ...