Course of Raku / Regexes and grammars / Regexes / Anchors

Word boundaries

Matching cat succeeds inside category, because the three letters really are there. Often that is not what you want — you mean the whole word cat. A word boundary anchor solves this.

• << matches at the left edge of a word (the start of a word)
• >> matches at the right edge of a word (the end of a word)

Wrap a word in these anchors to match it only as a complete word:

say 'the cat sat' ~~ /<< cat >>/;    # ｢cat｣
say so 'category'  ~~ /<< cat >>/;   # False

In category there is no word boundary right after cat, so the anchored pattern fails — exactly the behaviour we wanted.

A word boundary sits between a word character (\w) and a non-word character, so it does not consume anything itself; like ^ and $, it only asserts a position.

The two anchors can also be written with the guillemet characters « and » if you prefer them. They behave exactly like << and >>:

say 'the cat sat' ~~ /« cat »/;  # ｢cat｣
say so 'category'  ~~ /« cat »/;  # False

Course navigation

← Quiz — String anchors   |   Quiz — Anchors →

💪 Or jump directly to the exercises in this section.