Perlcompatible

Perlcompatible, short for Perl-compatible regular expressions (PCRE), refers to a family of regular expression libraries and syntax designed to be compatible with the features and syntax of Perl's regular expressions. The term is used to describe engines that implement a substantial subset of Perl 5's regex capability, enabling similar patterns, operators, and behaviors across languages and tools.

Origins and evolution: The PCRE library was created by Philip Hazel at the University of Cambridge and first released in the late 1990s. It became widely adopted as a reference implementation of Perl-compatible syntax. Over time, the project expanded to PCRE2, a modern rewrite that improves performance, memory management, and API stability. PCRE1 and PCRE2 are not binary compatible with each other, but aim to provide the same Perl-like feature set.

Features: Perl-compatible regex engines typically support backreferences, non-greedy and greedy quantifiers, character classes, alternation, grouping, and a rich set of assertions, including lookahead and lookbehind. They also support non-capturing groups, atomic groups, possessive quantifiers, and in some versions recursive patterns or conditional constructs. Unicode support and Unicode properties are commonly implemented. The exact feature set varies by version, with PCRE2 expanding support for large inputs and modern Unicode handling.

Usage and impact: PCRE and similar engines are used in many software systems, including PHP’s PCRE-based regex functions, nginx and Apache configuration tools, and various scripting languages and utilities. They are typically licensed under a BSD-like license.

See also: Perl Compatible Regular Expressions, PCRE, PCRE2.