Course of Raku / Regexes and grammars / Regexes / Matching strings

The match object

When a regex matches, the smartmatch returns a match object. The same object is also stored automatically in the special variable $/, which is sometimes called “the match variable”.

The match object is much more than a yes-or-no answer. As a string, it is the text that matched — either with the .Str method or with the prefix ~, which is the string-coercion operator and does exactly the same thing:

my $m = 'concatenate' ~~ /cat/;
say $m.Str; # cat
say ~$m;    # cat

It also knows where in the string the match was found. The .from method gives the position where it starts, and .to gives the position just after it ends:

my $m = 'room 7 left' ~~ /\d/;
say $m.Str;  # 7
say $m.from; # 5
say $m.to;   # 6

Positions are counted from zero, so the digit 7 sits at index 5.

When the regex does not match, the result is not a match object at all — it is the special value Nil. Assigning Nil to a scalar leaves it undefined:

my $m = 'abc' ~~ /z/;
say $m.defined; # False

So you can always check .defined (or just use the value in a Boolean context) before reading the matched text.

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