A regular expression (shortened as regex or regexp), sometimes referred to as rational expression, 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.
Regular expression techniques are developed in theoretical computer science and formal language theory. They are used in search engines, in search and replace dialogs of word processors and text editors, in text processing utilities such as sed and AWK, and in lexical analysis. Regular expressions are also supported in many programming languages.
Different syntaxes for writing regular expressions have existed since the 1980s, one being the POSIX standard and another, widely used, being the Perl syntax.
DFA regular expression library & friends
Onigmo is a regular expressions library forked from Oniguruma.
Henry Spencer's old regular expression library, also known as the book regex library, circa 1986.
clex is a simple lexer generator
A small implementation of regular expression matching engine in C
non-backtracking NFA-based regular expression library, for C and Python
An R interface to the Onigmo regular expression library
re1, the unbloated regexp engine by Russ Cox, elaborated to be useful for real-world applications
Golf is a programming language, framework and application server for high-performance web services and web applications, with focus on simplicity and memory safety..
Henry Spencer's BSD regular expression library. This is the original version, with a single bug fix. A modified version is in the rxspencer repository.
libag - The famous The Silver Searcher, but library 📚
Russ Cox/Rob Pike pikevm regex implementation
A modified version of Henry Spencer's BSD regular expression library. The original version is in the regex repository.
Walter Waldo's port of Henry Spencer's regular expression library from Tcl.
Lightweight, C-based regular expression engine as a single file library, inspired by the book "Beautiful Code."