Course of Raku / Regexes and grammars / Regexes / Quantifiers

Star, plus, and question mark

Three symbols cover the most common cases. Each one applies to the item right before it:

• * — zero or more times
• + — one or more times
• ? — zero or one time (optional)

The plus sign matches a run of one or more characters:

say 'aaah' ~~ / a+ /; # ｢aaa｣

It matched as many as as it could — three of them.

The star is like the plus but also succeeds when there is nothing to match, because zero repetitions are allowed:

say 'colour' ~~ / colou*r /; # ｢colour｣
say 'color'  ~~ / colou*r /; # ｢color｣

The question mark makes a piece optional — it matches whether or not the piece is there:

say 'colour' ~~ / colou?r /; # ｢colour｣
say 'color'  ~~ / colou?r /; # ｢color｣

Quantifiers apply to whatever comes immediately before them, including a character class. For example, \d+ matches a run of one or more digits — a whole number:

say 'order 66' ~~ / \d+ /; # ｢66｣

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