Syntax & Patterns

Regular expressions (RegExp) are patterns used for string matching.

Metacharacters (Special Characters)

• . → Matches any character except newline.
• ^ → Matches the start of a string.
• $ → Matches the end of a string.
• \\d → Matches any digit ([0-9]).
• \\w → Matches any word character ([a-zA-Z0-9_]).
• \\s → Matches whitespace.
• \\b → Matches a word boundary.
• \\ → Escapes a special character (e.g., \\. matches a dot .).

Quantifiers

• → 0 or more times (/a*/ matches "a", "aa", "").
• + → 1 or more times (/a+/ matches "a", "aa", but not "").
• ? → 0 or 1 time (/a?/ matches "a" or "").
• {n} → Exactly n times (/\\d{3}/ matches "123").
• {n,} → At least n times (/\\d{2,}/ matches "12", "123", "1234").
• {n,m} → Between n and m times (/\\d{2,4}/ matches "12", "123", "1234").

Groups & Character Classes

• (abc) → Capturing group (/(ab)+/ matches "abab").