Quantifiers, anchors & alternation

The building blocks — + * ? quantifiers, ^ $ anchors, and < a b > alternation.

Beyond literal text and metacharacters like \d, regexes are built from quantifiers (how many), anchors (where), and alternation (which of several).

Quantifiers and anchors #

+ means one-or-more, * zero-or-more, ? zero-or-one. ^ and $ anchor to the start and end of the string, so ^ a+ $ means "nothing but as".

say so "aaa" ~~ /^ a+ $/;
say so "" ~~ /^ a+ $/;

True
False

"aaa" is all as so it matches; the empty string fails because + needs at least one.

Alternation with < … > #

A quoted word list < cat dog > matches any one of its alternatives — a concise literal alternation.

for <cat dog fish> {
    say "$_: ", (/^ < cat dog > $/ ?? "pet" !! "other");
}

cat: pet
dog: pet
fish: other

Notes #

• < cat dog > is the literal-alternation shortcut; for general alternation of sub-patterns use || (first match) or | (longest match).
• Character classes: <[a..z]> matches one lowercase letter, <-[0..9]> matches one non-digit — the - negates the class.
• Backslash classes \d \w \s (and their negations \D \W \S) are the common shortcuts for digit, word-char, and whitespace.