MEPX
Chapter 4 of 10All chapters
  1. 1What a regex is
  2. 2Literals and classes
  3. 3Quantifiers
  4. 4Anchors and boundaries
  5. 5Groups and alternation
  6. 6Escaping
  7. 7Lookaround
  8. 8Flags
  9. 9When regex goes wrong
  10. 10Writing readable patterns

Chapter 4 of 10

Anchors and boundaries

Matching positions.

Start and end

A caret anchors to the start and a dollar to the end. With the multiline flag they anchor to each line rather than the whole string.

  • Anchoring a validation pattern at both ends is what stops a partial match passing.
  • A caret means start outside brackets and not inside them.

Word boundaries

The escape \b matches a position between a word character and a non-word character. It is why \bcat\b matches cat but not category.