Hernando Abella's Blog

What’s RegExp used for?

Hernando Abella's photo
Hernando Abella
·

2 min read

Regular Expressions are powerful tools to search, match, and manipulate text within strings. They are supported in various programming languages and text editors, making them an essential skill for any programmer or data analyst.

Practical examples using JavaScript:

  1. Validation: You can use regex to validate user input, such as email addresses, phone numbers, or passwords.
const email = "example@example.com";
const password = "Password123";

// Email validation
const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
const isValidEmail = emailRegex.test(email);
console.log("Is email valid?", isValidEmail);
// Output: true

// Password validation (at least 8 characters, including at least one letter and one number)
const passwordRegex = /^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$/;
const isValidPassword = passwordRegex.test(password);
console.log("Is password valid?", isValidPassword);
// Output: true

2. Search and Replace: You can find and replace specific patterns in a string.

const str = "Hello, World!";
const replacedStr = str.replace(/Hello/, "Hi"); 
// Output: "Hi, World!"

3. Splitting Strings: You can split a string into an array based on a specified delimiter or pattern.

const sentence = "The quick brown fox jumps over the lazy dog";
const words = sentence.split(/\s+/);
// Output: ["The", "quick", "brown", "fox", "jumps", "over", "the", "lazy", "dog"]

4. Extracting Information: You can extract specific information from a string.

const sentence = "My phone number is 123-456-7890";
const phoneRegex = /\b\d{3}-\d{3}-\d{4}\b/;
const phoneNumber = sentence.match(phoneRegex)[0];
// Output: "123-456-7890"

5. Replacing Forbidden Words: You can use regex to replace inappropriate or forbidden words in text, commonly used in profanity filters or content moderation.

const text = "This is a sentence with a bad word.";
const forbiddenWords = ["bad", "evil", "nasty"];
const regex = new RegExp(forbiddenWords.join("|"), "gi");
const cleanText = text.replace(regex, "****");
// Output: "This is a sentence with a **** word."

6. URL Manipulation: You can extract or modify parts of a URL using regex.

const url = "https://www.example.com/page?param=value";
const domainRegex = /^https?:\/\/([^/]+)/i;
const domain = url.match(domainRegex)[1];
// Output: "www.example.com"

Mastering regular expressions is an invaluable skill that requires time, practice, and dedication to master, but the benefits are immense. Through continuous learning and applying the knowledge you gain, you can unlock the full potential of pattern matching and become an expert in no time.

Regular expressions are the back-pocket tool of every computer scientist. They are powerful, versatile, and often overlooked, yet once mastered, they can make complex tasks seem trivial.” — Donald Knuth.

JavaScriptRegexprogramming