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Perl Compatible Regular Expressions (PCRE) is a library written in C, which implements a regular expression engine, inspired by the capabilities of the Perl programming language. Philip Hazel started writing PCRE in summer 1997. [ 3 ]
Raku rules are the regular expression, string matching and general-purpose parsing facility of the Raku programming language, and are a core part of the language. Since Perl's pattern-matching constructs have exceeded the capabilities of formal regular expressions for some time, Raku documentation refers to them exclusively as regexes, distancing the term from the formal definition.
The regular-expression engine uses a backtracking algorithm, extending its capabilities from simple pattern matching to string capture and substitution. The regular-expression engine is derived from regex written by Henry Spencer. The Perl regular-expression syntax was originally taken from Unix Version 8 regular expressions.
More generally, an equation E=F between regular-expression terms with variables holds if, and only if, its instantiation with different variables replaced by different symbol constants holds. [30] [31] Every regular expression can be written solely in terms of the Kleene star and set unions over finite words. This is a surprisingly difficult ...
The required syntactic condition α could be any valid context-free grammar fragment. More formally, a syntactic predicate is a form of production intersection, used in parser specifications or in formal grammars. In this sense, the term predicate has the meaning of a mathematical indicator function.
Perl Programming Documentation, also called perldoc, is the name of the user manual for the Perl 5 programming language. It is available in several different formats, including online in HTML and PDF. The documentation is bundled with Perl in its own format, known as Plain Old Documentation (pod).
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
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