Mastering Regular Expression Metacharacters: A Complete Guide

This article provides a comprehensive reference of common regular expression metacharacters and their usage. \: Marks the next character as a special character, text, backreference, or octal escape. For example, "n" matches the character "n"; "\n" matches a newline. ^: Matches the start of the input string. If the RegExp object's Multiline property is set, ^ also matches the position after "\n" or "\r". $: Matches the end of the input string. With Multiline enabled, $ also matches the position before "\n" or "\r". *: Matches the preceding character or subexpression zero or more times. +: Matches the preceding character or subexpression one or more times. ?: Matches the preceding character or subexpression zero or one time. {n}: n is a non‑negative integer; matches exactly n times. {n,}: n is a non‑negative integer; matches at least n times. {n,m}: n and m are non‑negative integers with n ≤ m ; matches between n and m times (inclusive). Note: no spaces are allowed between the numbers and the comma. ??: When this character follows another quantifier (*, +, ?, {n}, {n,}, {n,m}), it makes the quantifier non‑greedy, matching the shortest possible string. .: Matches any single character except "\n". Use a character class like "[\s\S]" to match any character including newlines. (pattern): Captures pattern as a subexpression; captured groups can be referenced with $0…$9. To match literal parentheses, escape them as "\(" or "\)". (?:pattern): Matches pattern without capturing it (non‑capturing group), useful for grouping with alternation. (?=pattern): Positive look‑ahead; asserts that pattern follows the current position without consuming characters. (?!pattern): Negative look‑ahead; asserts that pattern does not follow the current position. x|y: Matches either x or y . [xyz]: Character class; matches any one of the listed characters. [^xyz]: Negated character class; matches any character not listed. [a-z]: Character range; matches any character within the specified range. [^a-z]: Negated range; matches any character outside the specified range. \b: Word boundary; matches the position between a word character and a non‑word character. \B: Non‑word boundary; matches positions that are not word boundaries. \cX: Matches the control character indicated by X . \d: Digit character; equivalent to [0-9]. \D: Non‑digit character; equivalent to [^0-9]. \f: Form feed; equivalent to \x0c or \cL. \n: Newline; equivalent to \x0a or \cJ. \r: Carriage return; equivalent to \x0d or \cM. \s: Whitespace character (space, tab, form feed, etc.); equivalent to [ \f\n\r\t\v]. \S: Non‑whitespace character; equivalent to [^ \f\n\r\t\v]. \t: Tab character; equivalent to \x09 or \cI. \v: Vertical tab; equivalent to \x0b or \cK. \w: Word character (letters, digits, underscore); equivalent to [A-Za-z0-9_]. \W: Non‑word character; equivalent to [^A-Za-z0-9_]. \xNN: Hexadecimal escape where NN is a two‑digit hex code (e.g., \x41 matches "A"). \num: Matches a backreference num if that many capturing groups exist; otherwise, if num is an octal digit (0‑7), it is an octal escape. \n: Octal escape or backreference depending on preceding captures; if at least n groups exist, it is a backreference, otherwise an octal escape. \nm: Similar to \n, but with two digits; interpreted as a backreference if enough groups exist, otherwise as an octal value. \nml: Octal escape with three digits where n is 0‑3 and m , l are 0‑7. \uNNNN: Unicode escape; matches the character represented by the four‑digit hexadecimal number NNNN .