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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 .
regex - Henry Spencer's regular expression libraries ArgList: C BSD RE2: RE2: C++ BSD Go, Google Sheets, Gmail, G Suite Henry Spencer's Advanced Regular Expressions Tcl: C BSD RGX RGX : C++ based component library P6R RXP Titan IC: RTL Proprietary: hardware-accelerated search acceleration using RegEx available for ASIC, FPGA and cloud.
A string-searching algorithm, sometimes called string-matching algorithm, is an algorithm that searches a body of text for portions that match by pattern. A basic example of string searching is when the pattern and the searched text are arrays of elements of an alphabet ( finite set ) Σ.
Below is a simple grammar, defined using the notation of regular expressions and Extended Backus–Naur form.It describes the syntax of S-expressions, a data syntax of the programming language Lisp, which defines productions for the syntactic categories expression, atom, number, symbol, and list:
Regexp searches are restricted on the server, so this template reduces the regex search footprint by using the prefix: filter every time, restricting the search domain to a namespace at most. The prefix: parameter can further filter a namespace by specifying pagenames that start with a given letter(s).
The latter may allow its elements to be mutated and the length changed, or it may be fixed (after creation). A string is generally considered as a data type and is often implemented as an array data structure of bytes (or words ) that stores a sequence of elements, typically characters, using some character encoding .
String functions are used in computer programming languages to manipulate a string or query information about a string (some do both).. Most programming languages that have a string datatype will have some string functions although there may be other low-level ways within each language to handle strings directly.
For every long enough string in a regular language, there must be a middle section (y) that can be repeated (or pumped) any number of times to produce a string still in the language. In the theory of formal languages, the pumping lemma for regular languages is a lemma that describes an essential property of all regular languages.