my $text = '0101010101';
my %hash;
@hash{ split '', $text } = 1;
print scalar keys %hash, "\n";
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Although this code above will work correctly, it will not be doing so the way that you expected which could lead you to trouble.

@hash{@array} = $scalar
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only sets $scalar as the value for the first key in %hash. To set all the keys, you'd want to do something like:

@hash{@array} = ($scalar) x scalar @array;
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In the actual code above, since you don't check values anyway, you can just write:

@hash{@array} = ();
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