Regex Practical Patterns (Email, URL, Log Parsing)
Regex is great for finding and extracting patterns. It’s not great for fully validating complex standards (full RFC email/URL).
Email: “looks like an email”
^[^\s@]+@[^\s@]+\.[^\s@]+$
Find URLs in text (good enough)
https?:\/\/(?:www\.)?\S+
Log parsing (common building blocks)
ISO timestamp:
\b\d{4}-\d{2}-\d{2}[ T]\d{2}:\d{2}:\d{2}(?:\.\d+)?(?:Z|[+-]\d{2}:\d{2})?\b
Log level:
\b(INFO|WARN|WARNING|ERROR|DEBUG|TRACE|FATAL)\b
UUID:
\b[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}\b
Frequently Asked Questions
Can I use these patterns for full validation?
These patterns are designed for "looks like" checks, not full RFC compliance. For production validation, use dedicated libraries (email-validator, URL parser) that handle edge cases and international standards.
Why not use regex for full email validation?
Full email validation requires checking DNS records, handling international domains, and validating against RFC 5322—far beyond regex capabilities. Use regex for quick checks, dedicated libraries for validation.
What regex flavor do these patterns use?
These patterns work with JavaScript, Python, Java, and most regex engines. Some may need minor adjustments for specific engines (PCRE, .NET).
How do I test these patterns?
Use our Regex Tester tool to test patterns against your text, see matches highlighted, and debug issues in real-time.
When should I NOT use regex?
- Full email/URL validation (use dedicated libraries)
- Parsing HTML/XML (use proper parsers)
- Complex nested structures (use parsers)
- When readability matters more than conciseness (consider alternatives)
How do I escape special characters in regex?
Use backslash: \. for literal dot, \+ for literal plus, \* for literal asterisk. In character classes [], most characters don't need escaping except ], ^, -, and \.
