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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 .
In many programming languages, a particular syntax of strings is used to represent regular expressions, which are patterns describing string characters. However, it is possible to perform some string pattern matching within the same framework that has been discussed throughout this article.
5.5 Regular expression. ... Individual characters within a string can be accessed using the charAt method ... my_array = my_string. split ...
A parsing expression is a kind of pattern that each string may either match or not match.In case of a match, there is a unique prefix of the string (which may be the whole string, the empty string, or something in between) which has been consumed by the parsing expression; this prefix is what one would usually think of as having matched the expression.
The language extensively uses the string datatype, associative arrays (that is, arrays indexed by key strings), and regular expressions. While AWK has a limited intended application domain and was especially designed to support one-liner programs , the language is Turing-complete , and even the early Bell Labs users of AWK often wrote well ...
For example, the expression a < b < c tests whether a is less than b and b is less than c. [126] C-derived languages interpret this expression differently: in C, the expression would first evaluate a < b, resulting in 0 or 1, and that result would then be compared with c. [127] Python uses arbitrary-precision arithmetic for all integer operations.
For example, the set of characters matched by \w (word characters) is expanded to include letters and accented letters as defined by Unicode properties. Such matching is slower than the normal (ASCII-only) non-UCP alternative. Note that the UCP option requires the library to have been built to include Unicode support (this is the default for ...
In theoretical computer science and formal language theory, a regular language (also called a rational language) [1] [2] is a formal language that can be defined by a regular expression, in the strict sense in theoretical computer science (as opposed to many modern regular expression engines, which are augmented with features that allow the recognition of non-regular languages).