Course of Raku / Regexes and grammars / Regexes

Lookaround assertions

Sometimes you want to match something only because of what comes next to it, without making that neighbour part of the match. A lookaround assertion checks the text ahead of or behind the current position but does not consume it.

There are two directions — lookahead (what follows) and lookbehind (what precedes) — and each comes in a positive and a negative form. Like anchors, assertions match a position, not characters.

Topics in this section

• Lookahead
• Lookbehind

Practice

Complete the quizzes that cover the contents of this section.

• Quiz — Lookahead
• Quiz — Assertions

Exercises

This section contains 3 exercises. Examine all the topics of this section before doing the coding practice.

1. A bare number
2. Not followed by
3. Between brackets

Course navigation

← Solution: A whole word   |   Lookahead →