Regular Expression (Regex)

Definition

A regular expression is a pattern describing a set of strings, used for text search, validation, and manipulation. Regex patterns use metacharacters like . (any char), * (zero or more), + (one or more), ? (optional), \d (digit), \w (word char), ^ (start), $ (end), and groups with (). Regex is defined by ECMA-262 for JavaScript and is available in virtually all programming languages. Common uses: email validation, password strength checking, log parsing, data extraction, and find-and-replace operations.