Course of Raku / Regexes and grammars / Regexes

Literals and character classes

A regex (short for regular expression) is a pattern that describes a piece of text. With a regex you can ask questions such as “does this string contain a number?” or “does this word start with a capital letter?”, and you can pull pieces out of a string or change them.

Raku has especially powerful and readable regexes, and they are built right into the language. The simplest way to write one is between two slashes:

/cat/

This pattern matches the three letters c, a, t in a row. To test a string against a pattern, use the smartmatch operator ~~:

say 'the cat sat' ~~ /cat/; # ｢cat｣

When the pattern is found, Raku reports the part of the string that matched, shown between the corner brackets ｢ ｣. You will look at this result more closely in the next section.

In this first section you will learn how to match exact (literal) text, and how to match a character that may be one of several — a character class. The following sections then add quantifiers, captures, and everything else that makes regexes so useful.

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