Mastering Regular expression writing
on Cerebras Llama 3.1 70B

You are a Regular Expression Expert. Your goal is to provide concise and robust regular expressions. **Task:** Write a regular expression to match standard email addresses. The regex should ideally cover common email formats including subdomains, alphanumeric usernames, and popular top-level domains. Consider edge cases but prioritize common use. Explain your reasoning step-by-step. **Constraints:** * Must be a single regex pattern. * Avoid overly complex lookaheads/lookbacks unless absolutely necessary for correctness. **Output Format:** ```regex YOUR_REGEX_HERE ``` **Reasoning:** 1. Explain the username part. 2. Explain the '@' separator. 3. Explain the domain part. 4. Explain the TLD part. **Step-by-step thought process:** 1. **Analyze requirements:** Need to match standard email addresses, balancing robustness with complexity. 2. **Break down into components:** Username, '@', domain, TLD. 3. **Draft username pattern:** Start with `[a-zA-Z0-9._%+-]+`. This covers common characters. Need to ensure it doesn't start/end with special characters internally for basic validation, but for common use, this is a good start. 4. **Draft domain pattern:** `[a-zA-Z0-9.-]+`. Similar to username, allowing hyphens and dots. 5. **Draft TLD pattern:** `[a-zA-Z]{2,}` for at least two letters. Extend to `[a-zA-Z]{2,6}` for common TLDs or `[a-zA-Z]{2,}` for more general. 6. **Combine the parts:** `[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}`. 7. **Refine based on common standards:** Add a word boundary `\b` for safety. Consider stricter TLD rules. 8. **Final proposed regex:** `\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b` - (Self-correction: The pipe in `[A-Z|a-z]` means 'A-Z or | or a-z', which is incorrect. Should be `[A-Za-z]`). 9. **Final polished regex (internal thought):** `\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\b`. This looks good. It's robust for common cases without being overly strict for less common but valid email structures.