regexe

Regexe is a term used to describe regular expressions, a pattern-matching mechanism used to describe sets of strings for text processing. Regexe patterns are interpreted by specialized engines embedded in programming languages, editors, and command-line tools. They enable tasks such as searching for patterns, validating input, splitting text, and performing substitutions or extractions.

The concept of regular expressions has roots in formal language theory and gained practical prominence with tools like grep and later languages such as Perl, Python, and JavaScript. Today, regexe is a common facility across many platforms, though individual implementations may differ in syntax and features.

Core features of regexe include literals for exact characters, character classes like [abc], predefined classes such as \d, \w, and \s, and quantifiers such as *, +, ?, and {m,n}. Grouping with parentheses, alternation with |, and anchors like ^ and $ are routinely used. Escaping with backslashes is needed to treat metacharacters as literals. Many engines also offer advanced constructs such as non-greedy quantifiers, backreferences (\1, \2), and lookaround assertions (?=...), (?!...), with varying support for named groups and lookbehind.

Engine variations exist across PCRE, JavaScript’s ECMAScript, Python’s re module, Java’s java.util.regex, and .NET, among others. Differences can include support for lookbehinds, named groups, Unicode handling, and backtracking behavior. Practical considerations include performance and the potential for catastrophic backtracking on poorly designed patterns.

See also: Regular expressions, pattern matching, string processing.