What is regex

A regular expression - regex - is a tiny pattern that describes the shape of text you are looking for. Instead of writing a loop that walks the string character by character, you write one pattern and the engine finds every piece that fits. One pattern replaces a page of string-handling code.

Say you want every number in a line. The pattern is \d+: a digit, one or more times. The same pattern works in your editor, in grep, in a database, and in code:

The pattern is identical. Only the surrounding API differs - slashes and a g flag here, re.findall there. The skill is portable: the same patterns run in editors, databases, sed, grep, ripgrep, Python, JavaScript, Go, and Ruby.

It pays off in daily work: search-and-replace across a whole codebase, pulling emails, dates, and IDs out of logs, validating input, bulk-renaming files, and filtering output with grep or ripgrep. Learn it once and it follows you to every tool.

This course is hands-on. Each lesson is short, then you write a pattern until the tests turn green. Progress is saved in your browser - no signup, nothing to install. Start below.

These drills always match globally: every occurrence is highlighted, not just the first.