Regex Cheat Sheet for Backend Developers

Regular expressions (regex) are very important for backend developers working with Node.js, Python, Java, and databases. Indian developers often use regex for validation of phone numbers, Aadhaar, PAN, GST, emails, and passwords.

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1️⃣ Basic Regex Symbols

• . → Any character
• * → Zero or more
• + → One or more
• ? → Optional
• ^ → Start of string
• $ → End of string

Example: ^hello$

2️⃣ Character Classes

[abc]      → a or b or c
[a-z]      → lowercase letters
[A-Z]      → uppercase letters
[0-9]      → digits
[^0-9]     → not digits
\d         → digit
\w         → word character
\s         → whitespace

3️⃣ Common Validation Regex

Email Validation

^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$

Indian Phone Number

^(\+91)?[6-9][0-9]{9}$

PAN Card

^[A-Z]{5}[0-9]{4}[A-Z]$

GST Number

^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z][1-9A-Z]Z[0-9A-Z]$

PIN Code

^[1-9][0-9]{5}$

4️⃣ Regex in Node.js Example

const phoneRegex = /^(\+91)?[6-9][0-9]{9}$/;

console.log(phoneRegex.test("9876543210"));

Regex in Python

import re

pattern = r"^(\+91)?[6-9][0-9]{9}$"
print(re.match(pattern, "9876543210"))

5️⃣ Real Use Cases for Backend Developers

• Validate API input data
• Check password strength
• Extract log errors
• Parse CSV or JSON data
• Validate GST or PAN numbers

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6️⃣ Regex Interview Questions in India

• Write regex for email validation
• Find duplicate words in string
• Extract numbers from text
• Validate password rules

Tips to Master Regex

• Practice daily with real examples
• Test regex using online tools
• Start simple and build step-by-step
• Use comments to explain patterns

Conclusion

Regex is one of the most powerful skills for backend developers in India. It helps with validation, parsing, automation, and debugging.

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