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**
Combined from primary sources listed below.

In Regexes§

See primary documentation in context for General quantifier: ** min..max

To quantify an atom an arbitrary number of times, use the ** quantifier, which takes a single Int or a Range on the right-hand side that specifies the number of times to match. If a Range is specified, the end-points specify the minimum and maximum number of times to match.

say 'abcdefg' ~~ /\w ** 4/;      # OUTPUT: «｢abcd｣␤» 
say 'a'       ~~ /\w **  2..5/;  # OUTPUT: «Nil␤» 
say 'abc'     ~~ /\w **  2..5/;  # OUTPUT: «｢abc｣␤» 
say 'abcdefg' ~~ /\w **  2..5/;  # OUTPUT: «｢abcde｣␤» 
say 'abcdefg' ~~ /\w ** 2^..^5/; # OUTPUT: «｢abcd｣␤» 
say 'abcdefg' ~~ /\w ** ^3/;     # OUTPUT: «｢ab｣␤» 
say 'abcdefg' ~~ /\w ** 1..*/;   # OUTPUT: «｢abcdefg｣␤» 

Only basic literal syntax for the right-hand side of the quantifier is supported, to avoid ambiguities with other regex constructs. If you need to use a more complex expression, for example, a Range made from variables, enclose the Range in curly braces:

my $start = 3;
say 'abcdefg' ~~ /\w ** {$start .. $start+2}/; # OUTPUT: «｢abcde｣␤» 
say 'abcdefg' ~~ /\w ** {π.Int}/;              # OUTPUT: «｢abc｣␤» 

Negative values are treated like zero:

say 'abcdefg' ~~ /\w ** {-Inf}/;     # OUTPUT: «｢｣␤» 
say 'abcdefg' ~~ /\w ** {-42}/;      # OUTPUT: «｢｣␤» 
say 'abcdefg' ~~ /\w ** {-10..-42}/; # OUTPUT: «｢｣␤» 
say 'abcdefg' ~~ /\w ** {-42..-10}/; # OUTPUT: «｢｣␤» 

If then, the resultant value is Inf or NaN or the resultant Range is empty, non-Numeric, contains NaN end-points, or has minimum effective end-point as Inf, the X::Syntax::Regex::QuantifierValue exception will be thrown:

(try say 'abcdefg' ~~ /\w ** {42..10}/  )
    orelse say ($!.^name, $!.empty-range);
    # OUTPUT: «(X::Syntax::Regex::QuantifierValue True)␤» 
(try say 'abcdefg' ~~ /\w ** {Inf..Inf}/)
    orelse say ($!.^name, $!.inf);
    # OUTPUT: «(X::Syntax::Regex::QuantifierValue True)␤» 
(try say 'abcdefg' ~~ /\w ** {NaN..42}/ )
    orelse say ($!.^name, $!.non-numeric-range);
    # OUTPUT: «(X::Syntax::Regex::QuantifierValue True)␤» 
(try say 'abcdefg' ~~ /\w ** {"a".."c"}/)
    orelse say ($!.^name, $!.non-numeric-range);
    # OUTPUT: «(X::Syntax::Regex::QuantifierValue True)␤» 
(try say 'abcdefg' ~~ /\w ** {Inf}/)
    orelse say ($!.^name, $!.inf);
    # OUTPUT: «(X::Syntax::Regex::QuantifierValue True)␤» 
(try say 'abcdefg' ~~ /\w ** {NaN}/)
    orelse say ($!.^name, $!.non-numeric);
    # OUTPUT: «(X::Syntax::Regex::QuantifierValue True)␤»