I have a $number variable, and a $string, what is the fastest way to create a list of size $number that holds $string in each list entry?

Why by using the repetition operator in a list context of course

my $number = 4;
my $string = 'hello';
my @list   = ($string) x $number;

print @list;

__output__

hellohellohellohello
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See. the Multiplicative Operators section of perlop for more info on the repetition operator.
HTH

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broquaint