Regular Expression (Regex)

Regular expressions are patterns used to match character combinations in text. They are supported by virtually every programming language and are used for input validation, text search and replacement, data extraction, and parsing. The syntax includes literal characters, character classes, quantifiers, and anchors.

Common regex patterns include email validation, phone number matching, URL extraction, password strength checking, and data format validation. While regex can be extremely powerful, complex patterns can be difficult to read and maintain.

Key regex concepts include character classes ([a-z], \d, \w), quantifiers (*, +, ?, {n,m}), anchors (^, $), groups and capturing (()), lookahead and lookbehind, and flags (global, case-insensitive, multiline). Online regex testers are invaluable tools for building and debugging patterns interactively.