Copilot Regex Builder Skill

Description

## Copilot Regex Builder Skill

### Overview
Use Copilot to generate correct regular expressions from natural language descriptions, with explanations and test cases.

### Method 1: Comment-Driven Regex
Describe what you want to match in a comment:

```javascript
// Match email addresses: [email protected]
const emailRegex = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;

// Match US phone numbers: (123) 456-7890 or 123-456-7890 or 1234567890
const phoneRegex = /^\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}$/;

// Match ISO 8601 dates: 2024-01-15 or 2024-01-15T10:30:00Z
const isoDateRegex = /^\d{4}-\d{2}-\d{2}(T\d{2}:\d{2}:\d{2}(\.\d+)?(Z|[+-]\d{2}:\d{2})?)?$/;
```

### Method 2: Chat-Based Regex Generation
Ask Copilot Chat for complex patterns:

```
Create a regex that matches:
- URLs with http or https protocol
- Optional www subdomain
- Domain with 2-63 character labels
- Optional port number (1-65535)
- Optional path, query string, and fragment
- Should NOT match bare domains without protocol

Provide the regex with a breakdown of each part.
```

### Method 3: Regex Explanation
Paste an existing regex and ask Copilot to explain it:

```
Explain this regex step by step:
/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$/

Copilot explains:
- ^: start of string
- (?=.*[a-z]): positive lookahead for lowercase letter
- (?=.*[A-Z]): positive lookahead for uppercase letter
- (?=.*\d): positive lookahead for digit
- (?=.*[@$!%*?&]): positive lookahead for special character
- [A-Za-z\d@$!%*?&]{8,}: 8 or more of the allowed characters
- $: end of string
```

### Method 4: Test Case Generation
Ask Copilot to generate test cases for your regex:

```
Generate test cases for this email validation regex.
Include: valid emails, invalid emails, edge cases.
Format as a test array with { input, expected } objects.
```

### Common Regex Patterns

**Validation:**
- Email, phone, URL, IP address (v4 and v6)
- Date formats (ISO, US, EU), time, datetime
- Credit card numbers (Visa, Mastercard, Amex)
- Strong password requirements

**Extraction:**
- Extract URLs from text
- Parse CSV with quoted fields containing commas
- Extract hashtags and mentions from social media text
- Parse log file entries with timestamp, level, and message

**Replacement:**
- Sanitize HTML tags from user input
- Convert Markdown links to HTML anchor tags
- Normalize whitespace (multiple spaces to single)
- Mask sensitive data (email, phone, credit card)

### Tips
- Always test regex with edge cases before deploying
- Use named capture groups for readability: `(?<year>\d{4})`
- Prefer specific character classes over `.` to avoid over-matching
- Use non-greedy quantifiers `*?` and `+?` when appropriate
- Consider using a regex library for complex validations instead of raw regex

Free to copy and use. Compatible with GitHub Copilot, GPT-5.

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