Regex Fundamentals

Learn regular expressions from basics to advanced patterns with practical examples.

What are Regular Expressions?

Regular expressions (regex) are patterns used to match character combinations in strings. They are supported in most programming languages and text editors for search, validation, and text manipulation.

Basic Patterns

Literal characters match themselves. The dot (.) matches any single character. The asterisk (*) matches zero or more of the preceding element. The plus (+) matches one or more. Square brackets ([abc]) match any one of the enclosed characters.

Anchors and Groups

The caret (^) anchors to the start of a line, and the dollar sign ($) anchors to the end. Parentheses create capture groups for extracting matched portions. The pipe (|) acts as an OR operator between patterns.

Practical Examples

Use \d{3}-\d{3}-\d{4} to match US phone numbers, ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ to validate email addresses, and https?:\/\/[^\s]+ to find URLs in text.