Search results
Results from the WOW.Com Content Network
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.
find wildcard expressions and regular expressions. A search matches what you see rendered on the screen and in a print preview. The raw "source" wikitext is searchable by employing the insource parameter. For these two kinds of searches a word is any string of consecutive letters and numbers matching a whole word or phrase.
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 ...
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 closeness of a match is measured in terms of the number of primitive operations necessary to convert the string into an exact match. This number is called the edit distance between the string and the pattern. The usual primitive operations are: [1] insertion: cot → coat; deletion: coat → cot
The wildcard pattern (often written as _) is also simple: like a variable name, it matches any value, but does not bind the value to any name. Algorithms for matching wildcards in simple string-matching situations have been developed in a number of recursive and non-recursive varieties. [11]
Let c be the number of concatenation of the regular expression E and let s be the number of symbols apart from parentheses — that is, |, *, a and ε. Then, the number of states of A is 2s − c (linear in the size of E). The number of transitions leaving any state is at most two.