Overview

Regular Expressions Course

Learn regular expressions from first principles: literals, metacharacters, flags, capture groups, replacement, and a practical debugging workflow.

This course teaches regular expressions as pattern-matching programs—not as a feature tour of a regex tester. You will learn how engines interpret literals and metacharacters, what flags change, how capture groups power replacements, and how to debug patterns safely against realistic text.

Who this course is for

  • Developers writing validation, log parsing, or search-and-replace refactors
  • Engineers reading legacy code with dense /.../ patterns
  • Anyone who copied a regex from Stack Overflow and needs to understand why it fails on edge cases

What you will learn

  1. What a regex matches and where engines differ (JavaScript, PCRE, etc.)
  2. Literals, character classes, quantifiers, and anchors
  3. Flags such as g, i, m, s, and u
  4. Capture groups, backreferences, and replacement templates
  5. A debugging workflow with fixtures, highlights, and backtracking awareness

Use the related Regex Tester to try examples locally. A pattern that works on one sample is not proof it is correct for production input.

Start lesson 1
Regex Debugging With Fixtures, Flags, and Replace PreviewA practical workflow for testing regular expressions: sample lines, global and multiline flags, capture groups, and when to stop using regex.