Ekene Agunechemba

RegEx (Regular Expression) is a special pattern of characters used to search, match, and validate text—like checking if an email, phone number, or password follows the correct format.

Think of it as a smart filter that tells you: “Does this text follow the rule?” ✅ or ❌.

This is super useful when building sign-up forms for websites or apps, especially if you want to ensure users enter the correct information.

📝 Scenario: You’re the Developer

You’re building a registration form for an online platform in Nigeria. The form asks users for:

  1. Email Address
  2. Phone Number (Nigerian format)
  3. Password

Your job is to make sure users don’t enter incomplete, wrong, or unsafe data.

Let’s use RegEx to validate these inputs.

1. 📧 Validating Email Addresses

Emails must follow a format like someone@example.com.

✅ RegEx Pattern:

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

✅ What This Checks:

  • Characters before the @ (letters, numbers, dots, etc.)
  • A domain name after the @
  • A top-level domain like .com, .org, or .ng

🧪 Examples:

Input Valid?
myemail ❌ No @ or domain
me@gmail.com ✅ Yes
user@site.ng ✅ Yes

2. ☎️ Validating Nigerian Phone Numbers

Nigerian numbers start with prefixes like 070, 080, 081, 090, or 091, and they must be exactly 11 digits long.

✅ RegEx Pattern:

^(070|080|081|090|091)\d{8}$

✅ What This Checks:

  • Starts with allowed prefixes
  • Followed by exactly 8 digits (making 11 digits in total)

🧪 Examples:

Input Valid?
08012345678 ✅ Yes
0811234567 ❌ Only 10 digits
09187654321 ✅ Yes
0145678901 ❌ Starts with 01

3. 🔐 Validating Password Strength

You want users to create strong passwords. Your rules:

  • Minimum of 8 characters
  • At least 1 uppercase letter
  • At least 1 lowercase letter
  • At least 1 number
  • At least 1 special character

✅ RegEx Pattern:

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

✅ What This Checks:

  • (?=.*[a-z]) → has lowercase
  • (?=.*[A-Z]) → has uppercase
  • (?=.*\d) → has a digit
  • (?=.*[@$!%*?&]) → has a special character
  • {8,} → at least 8 characters total

🧪 Examples:

Input Valid?
password ❌ Weak (no caps, digits, or special chars)
Pass123 ❌ Less than 8 characters
Pa$$w0rd! ✅ Strong

🧠 Why Use RegEx Instead of if Statements?

Without RegEx, you’d write multiple lines like:

if (!email.includes("@")) { ... }
if (phone.length !== 11) { ... }

That gets messy fast. RegEx handles all those rules in just one line — clean, fast, and powerful!

✍️ Summary

Field RegEx Purpose
Email Ensures format like user@domain.com
Phone Number Confirms 11-digit Nigerian number with valid prefix
Password Enforces strong password rules

Whether you’re validating Nigerian numbers or building global platforms, RegEx will save you time and boost your form’s reliability.

✅ Review Questions

  1. Which RegEx pattern correctly validates a Nigerian phone number that starts with 081 and is 11 digits long? A) ^081\d{8}$ B) ^081\d{7}$ C) ^08\d{9}$ D) ^\d{11}$

  2. What will the following RegEx match?

    ^[a-zA-Z]+$

    A) Only numbers B) Only lowercase letters C) Only alphabetic characters (uppercase and lowercase) D) Any characters including special ones

  3. Which of these passwords will pass the RegEx validation for strength?

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

    A) password123 B) Pass1234 C) Pa$$w0rd D) admin@123

  4. True or False: A RegEx pattern like ^[a-zA-Z0-9._%+-]+@[a-z]+\.[a-z]{2,}$ will correctly match the email user@mail.com.ng.

  5. Write a RegEx to validate a Nigerian postal code (6-digit number). (Hint: Start with ^ and end with $)

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