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What Is a Regular Expression (Regex)?

A regular expression (regex or regexp) is a sequence of characters that defines a search pattern. Regex allows you to search, match, validate, extract, and transform text with incredible precision and flexibility. A single regex can replace dozens of lines of string-manipulation code.

Common Regex Use Cases

• Email validation: ^[\w.-]+@[\w.-]+\.[a-z]{2,}$
• Phone number extraction from text
• URL matching and parsing
• Finding all dates in a document
• Log file analysis — extracting error messages, IP addresses, timestamps
• Find-and-replace in code editors (VS Code, IntelliJ)
• Data cleaning — removing unwanted characters from CSV fields

Regex Pattern Quick Reference

• . — matches any single character
• * — zero or more of the preceding element
• + — one or more of the preceding element
• ? — zero or one of the preceding element
• ^ — start of string
• $ — end of string
• \d — any digit (0–9)
• \w — any word character (letters, digits, underscore)
• \s — any whitespace character
• [abc] — any character in the set
• (a|b) — a or b