name: regex_builder
router_kit: FullStackKit
description: Regular expression creation, testing, debugging and explanation guide.
metadata:
skillport:
category: development
tags: [accessibility, api integration, backend, browser apis, client-side, components, css3, debugging, deployment, frameworks, frontend, fullstack, html5, javascript, libraries, node.js, npm, performance optimization, regex builder, responsive design, seo, state management, testing, typescript, ui/ux, web development] - text-processing

🔤 Regex Builder

Regular expression creation and testing guide.

📋 Basic Syntax

Character Classes

Quantifiers

Anchors

🔧 Common Patterns

Email

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$

URL

https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)

Phone (TR)

^(\+90|0)?[0-9]{10}$

IP Address

^((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\.?\b){4}$

Date (YYYY-MM-DD)

^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])$

Password (Strong)

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$

🧪 Test Commands

JavaScript

const regex = /pattern/flags;
regex.test('string');      // true/false
'string'.match(regex);     // matches array
'string'.replace(regex, 'replacement');

Python

import re

re.search(r'pattern', 'string')
re.findall(r'pattern', 'string')
re.sub(r'pattern', 'replacement', 'string')

CLI (ripgrep)

rg 'pattern' file.txt
rg -o 'pattern' file.txt  # Only matching
rg -c 'pattern' file.txt  # Count

🔍 Debugging Tips

1. Escape special chars: . * + ? ^ $ { } [ ] ( ) | \
2. Lazy vs Greedy: .*? (lazy) vs .* (greedy)
3. Non-capturing group: (?:pattern)
4. Lookahead: (?=pattern) ve (?!pattern)
5. Lookbehind: (?<=pattern) ve (?<!pattern)

Regex Builder v1.1 - Enhanced

🔄 Workflow

Source: Regular-Expressions.info & OWASP ReDoS Prevention

Phase 1: Construction & Security

• [ ] Named Groups: Use named groups like (?<year>\d{4}) (Readability).
• [ ] ReDoS Prevention: Use Atomic Groups (?>...) or Possessive Quantifiers ++ to prevent "Catastrophic Backtracking".
• [ ] Boundaries: Always define string boundaries with ^ and $ (or \A and \z).

Phase 2: Testing & Validation

• [ ] Visual Testing: Visually test on Regex101 or RegExr.
• [ ] Unit Tests: Test both "match" (positive) and "non-match" (negative) cases.
• [ ] Performance: Keep regex execution time limited (Execution timeout).

Phase 3: Implementation

• [ ] Pre-compilation: Compile regex at start, not inside loops (new RegExp, re.compile).
• [ ] Comments: Use (?# comment) or "Verbose Mode" (Python re.X) for complex regexes.
• [ ] Library: Prefer ready-made libraries (URL parser, Email validator) for very complex patterns, do not reinvent the wheel.

Checkpoints