Settings
Test String
Results
About Regular Expressions
What is Regex?
Regular expressions (regex or regexp) are patterns used to match, find, and manipulate text. They consist of a sequence of characters defining a search pattern. First formalized in the 1950s by Stephen Kleene, regex is now a standard feature in virtually every programming language and text editor (JavaScript, Python, Java, Perl, etc.).
Common Use Cases
- Email Validation: Verify user email addresses during registration
- URL Matching: Extract URLs from text or validate URL formats
- Phone Numbers: Match and format international phone numbers
- Password Rules: Enforce complexity requirements (uppercase, numbers, symbols)
- Find & Replace: Bulk text replacements in code editors
- Log Analysis: Extract specific information from application logs
Real-World Examples
- Email Pattern: ^[^\\s@]+@[^\\s@]+\\.[^\\s@]+$ → Matches valid emails
- Phone Pattern: ^\\d{3}-\\d{3}-\\d{4}$ → Matches ###-###-####
- URL Pattern: https?://[^\\s]+ → Matches HTTP/HTTPS URLs
- Hex Color: ^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$ → Matches color codes
Regex Components
- \\d = digits (0-9)
- \\w = word characters (a-z, A-Z, 0-9, _)
- \\s = whitespace (spaces, tabs, newlines)
- . = any character (except newline)
- * = 0 or more times
- + = 1 or more times
- ? = 0 or 1 time